Starseige Tribes was massive and ridiculously fun on a 56k connection.
https://www.gamedevs.org/uploads/tribes-networking-model.pdf
In fact, I downloaded Tribes 2 a while back and was playing against bots just a few months ago.
The game is dated but it was still fun... in fact, I've often thought of trying to remake it in Unity or something!
Maybe one day.