sparkRT is the multitasking Operating System I utilized for my Spark Core research project (Connecting an Acoustic Guitar to the internet using Spark Core). It includes an adaptation of the Spark firmware, CoOS (CooCox OS) and my own extensions, all open source.
Here is a link to the Getting Started with sparkRTdocumentation and here is the link to download the Technical Reference manual
The entire archive can be downloaded here . The archive includes all the documentation
Enjoy!!!