Space station 13 is the best example.

It technically started closed source, but has been open source with countless forks existing in parallel for at least 90% of its lifetime.

AFAIK, SS13 had a number of source code leaks that resulted in popular forks as well. Not exactly the spirit of FOSS.

Not really. No servers based off of leaked source code have really lasted - they get nuked by the larger community.

The only ones I'm familiar with that people actually play for reasons other than the novelty/political statement of playing a FOSS game are ASCII roguelikes (most notably Nethack) and a menagerie of remakes of commercial games that have now surpassed the originals in features, graphics, and system compatibility (OpenTTD, OpenXCOM, etc.)

Not sure what qualifies as 'highly successful', 'from the start', etc. but Mindustry[0] is GPL, is actively updated, accepts and includes contributions from third parties and is available commercially.

[0] https://github.com/Anuken/Mindustry

Also it's fun, addicting, and pretty polished.