zzo38computer
today at 2:35 AM
I have written some useful small programs in uxn, such as: hex decoder in 39 bytes (which handles optional spaces and line breaks, uppercase and lowercase, etc), a program to convert JSON to NDJSON in 125 bytes, a program to convert DER to a subset of TER in 220 bytes, BLAKE2s in 1024 bytes (although some of it is padding for alignment, which is why it comes out to exactly 1024), a card game (including graphics, sound effects, fonts, scoring, etc) in 1853 bytes, etc. (These do not always check for errors (although the card game does check that you had made a valid move), which is one of the things that makes them short; since you might want such things sometimes that makes other programs longer, and this is not specific to uxn or to programs I wrote.) Other people might have also done.
The description of uxn and varvara are also small and might need only two pages (I did not write it).
I also remember reading in a book that someone made a game on Atari in 2 kilobytes, and described how they could make it fit (by making the map symmetric, etc), which was rejected because they had 4 kilobyte cartridges by then. (The article in this submission also links to a different game that (probably) someone else made in 2 kilobytes, but this time with JavaScript and HTML. Atari and uxn/varvara are much simpler systems than HTML/JavaScript, though.)
WalterBright
today at 6:42 AM
Hal Finney wrote a BASIC interpreter for the Mattel Intellivision in about 2K of ROM.
Of course, Hal was a genius.