Here are the historical versions:

• Ebba I Release 1 (tar.gz)
• Ebba II CVS
• Ebba H CVS (the version that the thesis reports on)

You might want to read my Master's Thesis if you want to play with Ebba.

The Savannah interface is available.

The Ebba Toolset implements a (variant of) the B formal method for software development originally developed by Jean-Raymond Abrial.