SM64 Simulator
Simulator for Super Mario 64 collision and movement
Initially, for the A Button Challenge, I ported Super Mario 64's collision engine over to JavaScript so that I could pop a REPL and do scripting (e.g. investigating potential spots in level geometry where glitchy behavior might be possible). I did this by going over every line of C in the relevant parts of the game's codebase and turning it all into JS by hand (with changes to make sure types stay accurate and floating-point math matches). Eventually, I kept adding and adding more of Super Mario 64 to this JS codebase, until I was able to use it as a brute-forcing tool for a tool-assisted speedrun competition.