Knock Out Rails & Rack Apps Like a Superhero. Pow is a zero-config Rack server for Mac OS X. Have it serving your apps locally in under a minute.
You may also be interested in ...
Delegated Events
A small, fast delegated event library for JavaScript.
Hexo
Hexo is a fast, simple and powerful blog framework. You write posts in Markdown (or other languages) and Hexo generates static files with a beautiful theme in seconds. Lot of plugins and themes available.
React Cosmos
React Cosmos is a developer tool that helps you build reusable React components.