itch.io

The sprites were mostly made by taking photographs against a black background, then erasing the black pixels to transparent. Some of the more complicated ones also used filters and manual erasing. The main image editing tool was GIMP, but there's nothing special about it for this purpose.

The game barely has an "engine" at all, just ordinary Javascript code. Keyboard inputs are read with keyup and keydown event handlers. Game logic frames are timed with setTimeout() and performance.now() and visual frames are timed with requestAnimationFrame(). Graphics are drawn to a 2d canvas context. Audio is played by starting and stopping audio HTML elements. (If you're wondering why index.html and index.js look more like compiler output and less like hand code, that's just from a minify script.)