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).
* http://sematext.com/spm - Free for 24h metrics, unlimited number of servers, 10 custom metrics, 500K 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 24h metrics, application performance management agents limited to one Java, one .NET, one PHP, and one Node.js
* 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 1000 documents. Free upgrade to Premium level for open-source projects.
* 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
* https://www.firebase.com/ - Build realtime apps, free plan has 50 Max Connections, 5 GB Data Transfer, 100 MB 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 512MB memory, 1GB storage). {[Browse one-click deployments](https://hub.openshift.com/)}.
* https://www.activestate.com/stackato/ - Enterprise-hardened Cloud Foundry PaaS from ActiveState, for private, public and hybrid cloud, free up to 20GB
* http://www.outsystems.com/ - Enterprise web development PaaS for on-premise or cloud, free "personal environment" offering allows for unlimited code and up to 1GB database.
* https://platform.telerik.com/ - Build and deploy mobile applications using Javascript. Free plan has 100 MB Data Storage, 1GB File storage, 5GB 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 1GB structured, 1GB unstructured, 1GB 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, 100MB of files and 100MB database storage each.
* http://apigee.com/docs/api-baas (product docs), http://apigee.com/docs/developer-vs-edge (registration) - Unlimited trial includes NoSQL data store with 25GB of storage, user and permission management, geolocation, 10,000,000 push notifications per 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.contentful.com - Content as a Service. Content Management & Delivery APIs in the cloud. 3 users, 3 spaces (repositories) and 1,000,000 API requests per month for free.
* http://www.kinvey.com - Mobile backend, starter plan has unlimited requests per second, with 2 GB of data storage, as well as push notifications for up 5,000,000 unique recipients. Enterprise application support.
* https://www.parse.com - Mobile backends, free plan has 30 requests per second, with 20 GB of file and database storage, as well as push notifications for up to 1,000,000 unique recipients.
* 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://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.visualstudio.com/products/what-is-visual-studio-online-vs - Unlimited free private code repositories; Tracks bugs, work items, feedback and more.
* 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 7500 images/month, 2gb storage, 5gb bandwidth.
* 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://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://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 {[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://codenvy.com/ - IDE in a browser, collaborative, git integration, build and run your app in customizable Docker-based runners (free 512Mb RAM to distribute between you runners), pre-integrated deploy to Google Apps.
* 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.
* 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 per 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.