Tsung - Tsung is an open-source multi-protocol distributed load testing tool.
OctoPerf - OctoPerf is a SaaS load testing solution, based on JMeter.
gatling - A high performance web server. Small! (125k static Linux-x86 binary with HTTP, FTP and SMB support).
StresStimulus - Load testing tool for websites and mobile that works with hard-to-test applications.
locust - An open source load testing tool written in Python.
SmartMeter.io - Performance Testing with Enterprise-Level Features with a familiar jMeter interface