What started a short list became quite a big description, more details inside the post.
Locust.io - an open source load testing tool. Define user behaviour with Python code, and swarm your system with millions of simultaneous users.
Workerman - a library for event-driven programming in PHP. Alternative to ReactPHP.
Trailblazer - a new Concept or a Domain Driven application structure for Rails. Tries to get rid of fat models, monolithic controllers, global helpers, etc.
ramjet - morph DOM elements from one state to another with smooth transitions