Geometry Dash is a rhythm platformer with one input: jump. Your cube slides forward at a fixed speed through a level built around a music track, and every spike, gap and gravity portal lands on a beat. Hit anything and you restart the level from the beginning — which sounds punishing until you realise a level is only about a minute long and you can retry instantly.
Robert Topala (RobTop) released it in 2013 and it has since become one of the most played games on the planet, partly because of its level editor and the community's absurdly hard user levels. This page runs a browser version of the core game — the official levels, the same physics and the same music timing — playable with the space bar or a click.
It plays the official levels with the same physics and music timing, which is what most people want from it. The mobile and Steam versions add the level editor and online user levels, which the browser build does not include.
Because every mistake restarts the level, and the levels are designed around exact musical timing. The difficulty is deliberate: the game is about memorising a level until you can play it cleanly, and the music makes that memorisation stick.
Yes. It is a 2D game that runs in the browser with nothing to install, and the space bar is the only control you need. Turn the sound on for the timing.