Selenium - Selenium automates browsers. That's it! What you do with that power is entirely up to you. Primarily, it is for automating web applications for testing purposes, but is certainly not limited to just that.
PublicAPIs - Explore the largest API directory in the galaxy
Screenster - 10x faster UI testing without a line of code.
The Unsplash API - No-limits, do-what-you-want API for access to 200K+ HD pics.
Robot framework - Robot Framework is a generic test automation framework for acceptance testing and acceptance...
API List - A collective list of APIs. Build something.