Here is some super-old version from 2004-2007:
https://github.com/alexknvl/fonlineApparently alexknvl cleaned it up a bit and fixed errors.
From the source code it looks like it used to be a team effort, but the team must have
been disbanded early on. There is quite a lot of Cvet code there and I wouldn't be too
surprised if some scraps of it was still in FOnline.
It should be pretty obvious that it has very little to do with "modern FOnline" made
by Cvet (you can't even open doors), but if you think about open source, it may (?)
be a good starting point, don't hold your breath for open sourcing the current one.