Red Ball 4 is one of the best-loved browser platformers, and Volume 1 is where it starts: you're a red ball rolling through side-scrolling levels, jumping gaps, squashing enemies and solving small physics puzzles — levers, crates, moving platforms.
The premise is that black square creatures are trying to flatten the world into cubes, which is exactly the right amount of story for a game like this. The physics are what carry it: the ball has real momentum, so stopping precisely is as much a skill as jumping.
Black square creatures are trying to turn the world into cubes, and you're a red ball rolling through physics-based levels to stop them.
By landing on them from above — the standard platformer approach, made trickier by the ball's momentum.
Yes — a light 2D game with nothing to install.