Annotation Studio is open source software, released under the GPL2 license.
The Rails application available on github at:
https://github.com/hyperstudio/Annotation-Studio
And our Data Store API Application (node.js and mongodb) is at:
https://github.com/hyperstudio/MIT-Annotation-Data-Store
Please feel free to fork it, and if you make changes you think others would find useful, submit a pull request!