Cornerstone is a front-end for Subversion, which is a version-control system for maintaining an ongoing history of changes to files. Programmers traditionally use version control for code projects, but it has become popular for people developing websites as well.

When I decided to switch from using CVS (the old standard of version control, but a bit long in the tooth these days) to Subversion, I needed a new front end for Subversion. (A lot of people use version control from the command line, but we're Mac users, after all, so give us a nice GUI!). Aside from some awkward, unfinished, or horrible Java-based interfaces, the only two options were Cornerstone and a beta version of something called Versions (which, to its credit, looked promising).

I picked up Cornerstone because it was clean, ready-to-use, and in active development. I have no regrets. The interface is excellent and very Mac-like, sufficiently flexible and customizable, and can handles duties both internally (diffs between versions) or with the help of external software (e.g. you want BBEdit to do my diffs).

Moving files, renaming directories, creating tags and branches uses Finder-like motions like option-dragging within the Cornerstone window.

A quick reference help section offers a nice crib sheet for the user interface, and the Help menu offers a directly embedded copy of the Subversion manual -- a nice touch for those of us not familiar with the depths of Subversion.

Support by email has been helpful and quick. My old CVS interface was free, so paying anything for a GUI like this might seem to be "too much," but $60 is a reasonable price for a solid piece of software that I use daily, and all day long.