SproutCore has several external frameworks created by developers in the community.  If you don't find a widget you need in SproutCore itself you may be able to find it here.  

To install most of these frameworks, just download or clone the code (if it is on Github) and place it in a "frameworks" directory inside of your project folder.  Then open your Buildfile and add it to your list of requires like so:

config :my_app, :required => [:sproutcore, :other_framework] 

If you have written a new framework, add a link to your code here and short description.

Widgets

• SCUI - Date Picker, Calendar, iGoogle-like Dashboard, Basic Drawing using Canvas, LinkIt framework for building directed graphs
• Flot-SproutCore - allows usage of Flot, a JavaScript charting library.  By Bo Xiao.
• Sai - [EXPERIMENTAL] A port of RaphaelJS to a more SproutCore-friendly environment
• Ki - A statechart framework for SproutCore

Data Sources

• SC-UDS - [EXPERIMENTAL] DataSources for Local Data Storage and Twitter
• OrionDB - A PHP REST database interface
• Thoth - A Node-based communications hub for multi-user SproutCore applications, serving as a unified database interface and automating distribution of data changes

Testing

• Lebowski- A test automation framework designed for full feature, integration, and regression testing of SproutCore applications.
• Jasmine-Sproutcore - A drop in replacement for QUnit using the Jasmine BDD test framework. 
• Simulo - Provides an adapter to easily simulate Sproutcore Events.
• Fictum - A stub server designed for use with Sproutcore, to it so that your tests do not have to hit a real server.