Special thanks to AlexMax for spending hours carefully converting our SVN repository to Mercurial and retroactively adding the license to the source history.
The Skulltag source is released under a 4-clause license based on the OSI-approved and GPL-compatible Sleepycat License, with the addition of the “No Endorsement” clause from the 3-clause New BSD License. Practically, this means that Skulltag source code is safe to use in either GPL or Doom Source License/Raven Source License/etc. source ports as long as the terms of the Skulltag license are satisfied.
Without further ado, here is the source.
PS: The fate of source versions older than 97c2 is unclear to me. My development time here began with the source of 97c2 and AFAIK Carnevil lost at least some of the older sources. I once got something that was labeled 96f source, I have no way to check if this actually is the 96f source or not though.