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.
Postman - The Collaboration Platform for API Development
Ranorex - Ranorex is a GUI test automation framework for testing of desktop, web-based and mobile applications.
Sauce Labs - Test mobile or web apps instantly across 700+ browser/OS/device platform combinations - without infrastructure setup.
TestComplete - TestComplete Desktop, Web, and Mobile helps you create repeatable and accurate automated tests across multiple devices, platforms, and environments easily and quickly.
Cucumber - Cucumber is a BDD tool for specification of application features and user scenarios in plain text.