Real 3D, real browser, no installer.
Most "3D browser game" search results are 2D games with isometric art. These two are actually 3D — rendered in WebGL with Three.js, running at sixty frames per second on anything newer than a 2020 laptop, and neither needs a download or an installer.
Parking Lot Zombie Apocalypse is a short-session driving game: you've got a car, a lot full of zombies, and a timer. It's the one to pick if you want something arcade-y and immediate. Space Flight 3D is the longer commit — first-person mining and combat around an asteroid field, with upgrades, a real economy, and sessions that stretch past twenty minutes if the run's going well.
Both work with keyboard and mouse. Mobile is playable for Parking Lot; Space Flight really wants a desktop.
Zombie-smashing vehicular mayhem
Dead Lot is a free browser-based 3D zombie driving game. Drive through a parking lot overrun with the undead, smash through increasingly brutal waves of zombies, and survive as long as you can. Your car is your only weapon — use speed and momentum to mow down hordes. Built with Three.js for smooth 3D graphics. No download required.
Mine. Fight. Evolve.
Ore Wars is a free browser-based 3D space mining and combat game. Pilot a mining vessel through an asteroid field, extract ore, sell it at a space station, and upgrade your ship with mining gear and weapons. As you progress, enemies appear and your ship evolves from Miner to Gunship to Cruiser. Built with Three.js. No download required.
If you have five minutes, Parking Lot. If you have an evening, Space Flight — it's the one that'll keep you coming back.