I have seen quite a few code bases, where the original author who didn't want to continue the project, just released the source code somewhere (as zlib, public domain, GPL or what ever) but nothing more.
If there was interest by some other developers, there was always some new open source project/community building itself up around the released code. And if not immediately, maybe a few years later.
E.g., some examples (where I was partly also involved in):
oh wow, I worked on puzzle pits for a while trying to get it to compile.
I ended up figuring out that the original binary ran perfectly fine in dosbox (which I played for a bit) and that the original code was pretty much useless and it would be easier to do a complete rewrite of the game to get it to work with a modern system. Not to mention this doesn't even use a recent standard version of C. So I ended up losing all motivation because of this and because of being a 1 man team.
It was a fun project though, it was this project that introduced me to the hacks that made dos games possible :)
If there was interest by some other developers, there was always some new open source project/community building itself up around the released code. And if not immediately, maybe a few years later.
E.g., some examples (where I was partly also involved in):
* OpenLieroX http://openlierox.net
* ioquake http://ioquake3.org/
* many projects here: http://icculus.org/projects/
* iodoom3: http://www.iodoom.org/ http://git.iodoom.org/ (still not much content there)
* https://github.com/id-Software
* Commander Genius: http://clonekeenplus.sourceforge.net/
* https://github.com/LaPingvino/The-Puzzle-Pits
...