What started a short list became quite a big description, more details inside the post.
awesome-selfhosted list. Selfhosting is the process of locally hosting and managing applications instead of renting from SaaS providers. This is a list of Free Software network services and web applications which can be hosted locally.
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.