Postman - The Collaboration Platform for API Development
Blazemeter - BlazeMeter is a self- service performance load testing cloud tool
Sauce Labs - Test mobile or web apps instantly across 700+ browser/OS/device platform combinations - without infrastructure setup.
flood.io - Load Testing for Everyone
TestComplete - TestComplete Desktop, Web, and Mobile helps you create repeatable and accurate automated tests across multiple devices, platforms, and environments easily and quickly.
gatling - A high performance web server. Small! (125k static Linux-x86 binary with HTTP, FTP and SMB support).