It is a tool that lets you perform queries on the contents of a CVS archive; you can: get a list of checkins, see what checkins have been made by a given person, or on a given CVS branch, or in a particular time period. It also includes tools for looking at checkin logs (and comments); doing diffs between various versions of a file; and finding out which person is responsible for changing a particular line of code ("cvsblame").

main Bonsai Query page

Here are some example queries that will give you a taste of what Bonsai is capable of:

Checkins to the Mozilla Source Mainline Module=MozillaSource Branch=HEAD
Checkins to the New Layout Mainline Module=Raptor Branch=HEAD
Checkins to the New Layout Integration Branch Module=MozillaSource Branch=RAPTOR_INTEGRATION0_BRANCH
Checkins to the Free Mail Source Branch Module=MozillaSource Branch=NORMANDY_BRANCH
Checkins to any branch of XFE by Ramiro between 26-Feb-1998 and 12-May-1998
Differences between revisions 3.1 and 3.3 of the file mozilla/cmd/xfe/forms.c

That's a small sample, but it should be enough to get you started. Play around with the various options on the main Bonsai Query page.