Caudium is backward compatible with Roxen Challenger 1.3. It has all the Roxen 1.3 RXML tags and the Roxen 1.3 API, so, from a technical point of view, it is quite the same (although Caudium has many improvements over Roxen 1.3). The main legal difference between Roxen 1.3 and Caudium is that Roxen is property of Roxen Internet Software whereas Caudium is owned by its developers, The Caudium Group. There are many functional extensions, improvements and bug fixes over the original Roxen 1.3 code base from which Caudium was created. Here you may say it is not a problem since it is under GPL. The problem is that even it is licensed under the GPL, RIS may not include your patch in its CVS tree, you may not have a CVS account, so you can't really do all you want. The main reason for the fork, however, was that RIS didn't pay attention to the users' needs, and proceeded to make the new versions of the Roxen Web Server largely incompatible with the previous versions, to the point where one couldn't switch to the new version of the software without much effort put into conversion of the old source code. Rewriting huge portions of RXML/Pike code just to switch to a new version of the web server seemed to be quite counter-productive, and thus the Caudium Project was born.