Just came across this cool video and project which aims to implement a Mecha game and SDK on the Quake1 engine (Darkplaces specifically):
You can find more details on their website and the Github repository.
Art assets are apparently not available yet due to some non-free placeholders, but I hope this will be changed soon. Also no multiplayer, but that might be possible to fix.
Also really cool would be a Occulus Quest VR port via the already available and quite awesome Darkplaces VR port called QuakeQuest.
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