yepnope.js : A Conditional Loader For Your Polyfills!
TraceKit : Not all browsers support stack traces on error objects, but TraceKit squeezes out as much useful information as possible and normalizes it.
Crafty : JavaScript Game Engine, HTML5 Game Engine
Slate : Slate is a completely customizable framework for building rich text editors.
Slate lets you build rich, intuitive editors like those in Medium, Dropbo...
PeerJS : Peer-to-peer data in the web browser.
PeerJS completes WebRTC as an API abstraction, connection broker, and binary serialization format
Namespace.js is a small javascript script which provide namespacing utilities. It is framework independent. It also allows you to remotely include files.