Built for developers and testers alike, SoapUI is the only open source tool that covers the entire testing spectrum (functional, security, load, mocking).

Best "simple" screen capturing app (Mac and Windows) because it creates animated gifs that attach to bugs easily. Simple because it works a lot like snippy to capture screen areas

Robotium is an Android test automation framework that has full support for native and hybrid applications.

A screenshot/screenvideo tool! Also allows you to do basic alterations to the screenshots (arrows, blur, ...)

Robot Framework is a generic open source automation framework. It can be used for test automation and robotic process automation (RPA).

Free and open source. Solve accessibility issues before they reach your customers.