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

Free & OpenSource REST API Testing Tool for all levels in a Test Pyramid

The Cyber Swiss Army Knife - a web app for encryption, encoding, compression and data analysis. Built and maintained by GCHQ (The UK intelligence and security organisation).

The Apache JMeter™ application is open source software, a 100% pure Java application designed to load test functional behavior and measure performance. It was originally designed for testing Web Applications but has since expanded to other test functions.

Automation Test Reporting. OSS, Language & Framework agnostic

The first and most popular cookie editor extension for Google Chrome and Opera