Nidhogg [official site] is one of the very finest local multiplayer games. The two-player swordfighting duel always drawn some of the biggest crowds at events I’ve helped run, delighting folks with desperate gambits and deathworm devourings even after it escaped the event scene and got a proper home release in 2014. That version also brought online multiplayer and… well, Nidhogg was not one of the very finest online multiplayer games.
It’s in better shape now, though, as developers Messhof have worked with another programmer to improve its latency and desync issues. The fruit of their labour, a new patch, is now out.