locust

Tests are written in regular Python code, allowing use of loops, conditionals, and standard libraries without callbacks or XML, as shown in the example code snippet for defining user behavior.

Uses event-based gevent to handle hundreds of thousands of concurrent users and supports running tests over multiple machines, enabling testing of highly concurrent systems as highlighted in the README.

Includes an interactive web interface for live monitoring and dynamic load adjustment during tests, with screenshots in the README showing real-time charts and statistics.

Can test any system by writing custom clients or using community extensions, making it adaptable beyond HTTP, though this requires additional effort as noted in the documentation links.