The source code is located at Google Code. However, you have to select the proper repository in the 'Repository' drop-down in the upper left corner of the 'Source' web page.

For your convenience:

http://code.google.com/p/text20/source/checkout?repo=plugin http://code.google.com/p/text20/source/checkout?repo=trackingserver http://code.google.com/p/text20/source/checkout?repo=diagnosis http://code.google.com/p/text20/source/checkout?repo=peep