I'm late to this party but OpenDivX Version 4 Alpha 48 was released about two weeks ago. The new features are listed in this log. OpenDivX is the stylish MPEG4-based open source codec that aims to be more than the flavor of the month. Here is the introduction from Project Mayo:
Our first and cornerstone project, if you like DivX™, you'll love OpenDivX. DivX is now of the people, by the people, and for the people! We love DivX so much, we're setting it free. OpenDivX™ is an open source project, and anyone is free to work on it, subject to the terms of this legal mumbo jumbo. Take a look at the CVS tree, and read the documentation. Come one, come all. Find out how to get involved. You can also read about why we did this, if you're so inclined.
It supports operating systems as diverse as Windows, Linux, and Amiga. More can be found here