Quake III Arena is the arena shooter distilled. id Software released it in 1999 with no story and no campaign — just maps, bots and other players, with weapons balanced for one thing: fast, precise, unforgiving duels. The rocket launcher, the rail gun and the lightning gun are still the reference point for every arena shooter since.
Movement is the skill. Strafe-jumping to build speed, rocket-jumping to reach a platform, and controlling the armour and weapon spawn timings mattered more than aim at the top level. This browser build runs the demo, which is enough to feel exactly why.
It's the demo, running in the browser. The full game is sold on Steam and other stores.
Firing a rocket at your own feet while jumping. The splash damage launches you much higher and further than a normal jump, at the cost of some health — it's how you reach platforms and escape fights.
Yes — it's a 1999 game and runs comfortably in a browser with nothing to install.