Activision and Raven Software just released the full source code to their games Jedi Academy and Jedi Outcast for people to mess around with. Although I’ve never played either of them, I can’t pass up an opportunity like this! Of note is that they seem to have engineered everything pretty much from the ground up, including asset management, graphics, multiplayer, security, etc. etc. etc. (you name it, it’s in there).
You can also find a GitHub mirror here — although they seem to be modifying the code to “maintain and improve” it. For the original sources it’s best to check out the SourceForge links above.
And for anyone concerned about licenses and such, it’s released under GNU GPLv2.