Trax is a general object versioning system for Squeak.  It is capable of versioning any object that can be serialized.  Additionally, there is an extension that makes it possible to version Monticello Smalltalk source code packages.  I also created an N-way merge tool for merging multiple versions of a Monticello source code package.  Follow the links below to view a few screenshots (with descriptions of what you are looking at), a video demo (that includes a brief overview of the code), and the downloads.  Additionally, please be sure to review the software license for Trax.
The following screenshot shows the Trax version browser.