Developers and Open Source authors now have a massive amount of services offering free tiers, but it can be hard to find them all in order to make informed decisions.
The scope of this particular list is limited to things infrastructure developers (System Administrator, DevOps Practitioners, etc.) are likely to find useful. We love all the free services out there, but it would be good to keep it on topic. It's a bit of a grey line at times so this is a bit opinionated; do not be offended if I do not accept your contribution.
You can help by sending Pull Requests to add more services. Once I have a good set of links in this README file, I'll look into a better layout for the information and links (help with that is appreciated too).
* [Cloud Source Repositories](https://cloud.google.com/tools/cloud-repositories/) - Free private GIT repositories hosted on Google Cloud Platform. Supports syncing with existing GitHub and Bitbucket repos. Free Beta for up to 500 MB of storage
* https://yammer.com/ - Private social network standalone or for MS Office 365. Free, just a bit less admin tools and users management features
* https://www.blockspring.com/ - Share scripts with anyone on your team: cross language and with spreadsheet users. Free for 5 million runs/month
* https://helpmonks.com/ - Shared inbox for teams - Free for open source projects and non-profit organizations
* http://typetalk.in/ - Share and discuss ideas with your team through instant messaging on the web or on your mobile
* https://talky.io/ - Free group video chat. Anonymous. Peer‑to‑peer. No plugins, signup, or payment required
* http://sourcetalk.net/ - Code discussion tool, free for open code talks
* http://vipaar.com/ - Help over video with augmented reality. Free without analytics, encryption, support
* https://evernote.com/ - Tool for organizing information. Share your notes and work together with others
* https://www.wunderlist.com/ - Share your lists and work collaboratively on projects with your colleagues - Available for free to download and use on iPhone, iPad, Mac, Android, Windows and the Web
* http://doodle.com/ - The scheduling tool you'll actually use. Find a date for a meeting 2 times faster
* https://codenvy.com/ - Share developer environments for your project. Includes configuration for the browser IDE, build, debug and run environments. Free tier with 4 GB environments and support for 90+ languages
* http://wistia.com/ - Video hosting with viewer analytics, HD video delivery, and marketing tools to help understand your visitors. 25 Videos and Wistia branded player.
* https://www.onelogin.com/ - Identity as a Service (IDaaS), Single Sign-On Identity Provider, Cloud SSO IdP, 3 company apps and 5 personal apps, unlimited users
* http://sematext.com/spm - Free for 24 hours metrics, unlimited number of servers, 10 custom metrics, 500 K custom metrics data points, unlimited dashboards, users, etc
* https://sealion.com/ - Free up to 2 servers, 3 days data retention, graphs and raw command output history (`top`, `ps`, `ifconfig`, `netstat`, `iostat`, `free`, custom, etc.)
* https://www.appdynamics.com/ - Free for 24 hours metrics, application performance management agents limited to one Java, one .NET, one PHP, and one Node.js
* https://deadmanssnitch.com/ - Monitoring for cron jobs. 1 free snitch (monitor), more if you refer others to sign up
* http://apimetrics.io/ - Automated API Performance Monitoring, Testing and Analytics. Free Plan - Manually make API calls and Run from their West Coast servers
* https://www.opsdash.com/ - Self-hoster server, clusters and services monitoring, free for 5 servers and 5 services
* https://rollbar.com/ - Exception and error monitoring, free plan - 5,000 errors/month, unlimited users, 30 days retention
* https://bugsnag.com/ - Free for up to 2,000 errors/month after the initial trial
* https://airbrake.io/ - Automatically groups, organizes and notifies you about your application errors. Free plan - 7,200 errors/day, 1 user, 1 project, 2 days retention
* https://www.algolia.com/ - Hosted search-as-you-type (instant). Free hacker plan up to 1,000 documents and 50,000 operations. Bigger free plans available for community/open source projects
* https://swiftype.com/ - Hosted search solution (API and crawler). Free for a single search engine with up to 1,000 documents. Free upgrade to Premium level for open-source projects
* http://sendgrid.com/ - 400 emails/day for free and 25,000 free transactional emails/month for emails sent from a Google compute instance or Microsoft Azure App Service
* https://developers.google.com/speed/libraries/ - The Google Hosted Libraries is a content distribution network for the most popular, open-source JavaScript libraries
* https://www.asp.net/ajax/cdn/ - The Microsoft Ajax Content Delivery Network (CDN) hosts popular third party JavaScript libraries such as jQuery and enables you to easily add them to your Web application
* http://restlet.com/products/apispark/ - APISpark enables any API, application or data owner to become an API provider in minutes via an intuitive browser interface
* https://cloud.google.com/appengine/ - Google App Engine gives 28 instance hours free, 1 GB NoSQL Database and more
* https://www.firebase.com/ - Build realtime apps, free plan has 100 max. connections, 10 GB data transfer, 1 GB data storage, 1 GB hosting storage and 100 GB hosting transfer
* https://www.openshift.com/ - Red Hat PaaS, free tier provides three small gears each with 512 MB memory and 1 GB storage. {[Browse one-click deployments](https://hub.openshift.com/)}
* https://algorithmia.com/ - Host and Use algorithms for free - includes 10,000 credits (seconds of on-demand execution time) free. Now with CLI support
* https://bigml.com/ - Hosted machine learning algorithms. Unlimited free tasks for development, limit of 16 MB data/task
* https://www.activestate.com/stackato/ - Enterprise-hardened Cloud Foundry PaaS from ActiveState, for private, public and hybrid cloud, free up to 20 GB
* http://www.outsystems.com/ - Enterprise web development PaaS for on-premise or cloud, free "personal environment" offering allows for unlimited code and up to 1 GB database
* https://platform.telerik.com/ - Build and deploy mobile applications using JavaScript. Free plan has 100 MB data storage, 1 GB file storage, 5 GB bandwidth, 1 million push notifications for BaaS offering, 100 active devices for analytics
* http://scn.sap.com/docs/DOC-56411 - The in-memory Platform-as-a-Service offering from SAP. Free developer accounts come with 1 GB structured, 1 GB unstructured, 1 GB of GIT data and allow you to run HTML5, Java and HANA XS apps
* https://www.mendix.com/ - Rapid Application Development for Enterprises - Unlimited number of free sandbox environments supporting 10 users, 100 MB of files and 100 MB database storage each
* https://www.tutum.co/ - The Docker Platform for Dev and Ops - Build, deploy, and manage your apps across any cloud - free while in beta and free developer plan when tutum will be production ready
* http://apigee.com/docs/api-baas (product docs), http://apigee.com/docs/developer-vs-edge (registration) - Unlimited trial includes NoSQL data store with 25 GB of storage, user and permission management, geolocation, 10,000,000 push notifications/month, remote configuration, beta and A/B split testing, APM, fully API driven. Accessible and manageable via UI, SDK, and API
* https://bip.io/ - A web-automation platform for easily connecting web services. Fully open GPLv3 to power the backend of your open-source project. Commercial OEM License available
* https://www.blockspring.com/ - Cloud functions. Free for 5 million runs/month
* https://www.contentful.com/ - Content as a Service. Content management and delivery APIs in the cloud. 3 users, 3 spaces (repositories) and 1,000,000 API requests/month for free
* http://www.kinvey.com/ - Mobile backend, starter plan has unlimited requests/second, with 2 GB of data storage, as well as push notifications for up 5,000,000 unique recipients. Enterprise application support
* http://konacloud.io/ - Web and Mobile Backend as a Service, with 5 GB free account
* https://layer.com/ - The full-stack building block for communications
* https://www.parse.com/ - Mobile backends, free plan has 30 requests/sec, with 20 GB of file and database storage, as well as push notifications for up to 1,000,000 unique recipients
* http://www.dreamfactory.com/ - DreamFactory is an open source backend platform that provides all of the RESTful services you need to build fantastic mobile and web applications
* https://www.mashape.com/ - API Marketplace And Powerful Tools For Private And Public APIs. With the free tier, some features are limited such as monitoring, alerting and support
* http://closeheat.com/ - Development Environment in the Cloud for Static Websites with Free Hosting and GitHub integration. 1 free website with custom domain support
* https://www.simplybuilt.com/ - SimplyBuilt offers free website building and hosting for open source projects (http://www.simplybuilt.com/explore/free-websites-for-open-source-projects). Simple alternative to GitHub Pages
* https://import.io/ - Easily turn websites into APIs, completely free for life
* https://kimonolabs.com/ - "Turn websites into structured APIs from your browser in seconds", free for public APIs, up to 20 million pages fetch/month. Supports scheduling, JSON, CSV, post-auth,...
* https://www.cloudamqp.com/ - RabbitMQ as a Service. Little Lemur plan: max 1 million messages/month, max 20 concurrent connections, max 100 queues, max 10,000 queued messages, multiple nodes in differen AZ's
* https://cacoo.com/ - Online diagrams in real time: flowchart, UML, network. Free max. 15 users/diagram, 25 sheets
* https://www.draw.io/ - Online diagrams stored locally, in Google Drive, OneDrive or Dropbox. Free for all features and storage levels
* https://hub.jazz.net/ - IBM Bluemix's project management services. Free for public projects, free for up to 3 users for private projects
* http://leankit.com/ - Kanban board, that visualizes your workflow. Free up to 10 users
* https://www.visualstudio.com/products/what-is-visual-studio-online-vs - Unlimited free private code repositories; Tracks bugs, work items, feedback and more
* https://testlio.com/ - Issue tracking, test management and beta testing platform. Free for private use
* http://www.targetprocess.com/ - Visual project management, from Kanban and Scrum to almost any operational process. Free for unlimited users, up to 1,000 data entities (more details at http://www.targetprocess.com/pricing/)
* http://cloudinary.com/ - Image upload, powerful manipulations, storage, and delivery for sites and apps, with libraries for Ruby, Python, Java, PHP, Objective-C and more. Perpetual free tier includes 7,500 images/month, 2 GB storage, 5 GB bandwidth
* https://plot.ly/ - Graph and share your data. Free tier includes unlimited public files and 10 private files
* https://transloadit.com/ - Handles file uploads & encoding of video, audio, images, documents. Free for open source & other do-gooders. Commercial applications get the first GB free for test driving
* https://podio.com/ - You can use Podio with a team of up to five people and try out the features of the Basic Plan - except User Management
* https://placehold.it/ - A quick and simple image placeholder service
* https://placekitten.com/ - A quick and simple service for getting pictures of kittens for use as placeholders
* http://placepenguin.com/ - A quick and simple service for placeholder images of penguins
* http://embed.ly/ - Provides APIs for embeding media in a webpage, Responsive image scaling, extracting elements from a webpage. Free for up to 5,000 URLs/Month at 15 requests/sec
* https://backhub.co/ - Backup and archive your GitHub repositories. Free for public repos
* http://www.otixo.com/ - Encrypt, share, copy and move all your cloud storage files from one place. Basic plan provides unlimited files transfer with 250 MB max file size limit and allows 5 encrypted files
* https://c9.io/ - IDE in a browser. Incorporates an Ubuntu virtual machine and in-browser terminal access. Integrates with GitHub and BitBucket, but also adds SFTP and generic GIT access
* https://codeanywhere.com/ - Full IDE in the browser and mobile apps. Access FTP, SFTP, Dropbox, Google Drive, GitHub, and BitBucket. Hosted virtual machines with terminal access. Collaboration features like share links, live editing, permissions, and version tracking
* https://codenvy.com/ - IDE and automated developer workspaces in a browser, collaborative, GIT/SVN integration, build and run your app in customizable Docker-based runners (free tier includes: 4 GB RAM, always-on machines, ability to run multiple machines simultaneously), pre-integrated deploy to Google Apps
* https://koding.com/ - IDE in a browser. Features: Full sudo access - VMs hosted on Amazon EC2 - SSH Access - Real EC2 VM, no LXCs/hypervising - Custom sub-domains - Publicly accessible IP - Ubuntu 14.04 - IDE/Terminal/Collaboration
* https://www.nitrous.io/ - Private Linux instance(s) with interactive collaboration, free for 2 hours/day. {[More Details](http://goo.gl/J1Zbsg)}
* http://visualstudio.com/free - Fully-featured IDE with thousands of extensions, cross-platform app development (Microsoft extensions available for download for iOS and Android), desktop, web and cloud development, multi-language support (C#, C++, JavaScript, Python, PHP and more)
* https://cloud.sagemath.com/ - Collaborative mathematics-oriented IDE in a browser, with support for Python, LaTeX, IPython Notebooks, etc
* https://apiary.io/ - Collaborative design API with instant API mock and generated documentation (Free for unlimited API blueprints and unlimited user with one admin account and hosted documentation)
* https://www.mockable.io/ - Mockable is a simple configurable service to mock out RESTful API or SOAP web-services. This online service allows you to quickly define REST API or SOAP endpoints and have them return JSON or XML data
* https://www.jetbrains.com/products.html - Productivity tools, IDEs and deploy tools. Free license for students, teachers, open source projects, and user groups
* http://www.tadpoledb.com/ - IDE in browser Database tool. Support Amazon RDS, Apache Hive, Apache Tajo, CUBRID, MariaDB, MySQL, Oracle, SQLite, MSSQL, PostgreSQL and MongoDB databases
* https://www.sourcelair.com/ - In-browser IDE for Django, JavaScript, HTML5, Python, and more. Integrates with GIT, Mercurial, GitHub, Heroku and more. Free forever for 1 private project
* https://codepen.io/ - CodePen is a playground for the front end side of the web
* https://www.cognalys.com/ - Freemium mobile number verification through an innovative and reliable method than using SMS gateway. Free accounts will have 70 tries and 50 verifications/day. {[Signup](https://www.cognalys.com/signup/1)}
* https://www.braintreepayments.com/ - Credit Card, Paypal, Venmo, Bitcoin, Apple Pay,... integration. Single and Recurrent Payments. First $50 are free of charge
* http://taxratesapi.avalara.com/ - Get the right sales tax rates to charge for the close to 10,000 sales tax jurisdictions in the USA. Free REST API. Registration required
* https://www.tutum.co/ - The Docker Platform for Dev and Ops - Build, deploy, and manage your apps across any cloud - free while in beta and free developer plan when tutum will be production ready
* https://www.fullcontact.com/developer/pricing/ - Help your users know more about their contacts by adding social profile into your app. 500 free Person API matches/month