Yes, it bears a resemblance to FileMerge, but Changes offers features and options well beyond Apple's aging utility. Because it uses existing systems (chdiff) and provides a plugin SDK, it's both easy to implement and extensible. The command line utility and F-Script support provide additional options for incorporating Changes into your existing workflow. I appreciated the familiar interface and was impressed by how simple it was to integrate Changes into my existing TextMate/Subversion workflow with a few keystrokes.
Changes, which is a Leopard-only release, is currently in beta and is available for immediate download. As of today, the download requires registering for a beta key but the developer has let us know that an upcoming build will switch to a simple time-locked beta. If you dig the software you can get a pre-release discount on a full license, receiving $10 off the $39.95 release price, but the offer is only good until the end of the beta period. And, less importantly, I made it through the whole post without a Bowie reference. Phew.
Update: The new build mentioned above has been released and no longer requires registering for a beta key. An email address is still required for download, but it's less hassle now.