Maze - Beautiful & actionable analytics for InVision prototypes
ExpressJS - Sinatra inspired web development framework for node.js -- insanely fast, flexible, and simple
Conversion Crimes - Get insights on how users behave on your site or software and how they feel about it. Remove friction and increase motivation to buy.
Famous Engine - The Famous Engine is a free and open source JavaScript rendering engine.
Koncept - Usability testing, interactive prototypes & metrics
Chart.js - Easy, object oriented client side graphs for designers and developers.