Acorn Risc PC, 1996 · running in your browser from the original code
The map editor runs in your browser too: 30 tile types, gems, monsters, switches and teleports, with the original 35 levels to learn from. A finished pack is just a link, so sharing it is one copy and paste. Open it on a phone and it works there as well.
Guide the Thing around the tiles, grab every gem and get out before the timer runs out. Fall off the edge and you lose a life. Each level ends with a password so you can come back later.
The game shipped as 40 KB of hand-written ARM code plus four third-party modules (FastSpr, Amnesia, Blitz and Stasis). None of that was changed: a small 26-bit ARM interpreter written in C and compiled to WebAssembly runs it as-is, and the handful of RISC OS calls the game makes (screen banks, keyboard scan, file loads, the sound channel handler) are provided by the host page.
Screen is MODE 13, 320×256 in 256 colours, 50 frames a second. Sound is the original 8-bit logarithmic VIDC samples, mixed at 20.8 kHz.