I just finished my useless Brainfuck compiler ( https://news.ycombinator.com/item?id=44087363 ) and was thinking of a more novel application that hasn't been done already, like going the other direction and turning RISC-V assembly back to Brainfuck code. Currently trying to get MD5 work...

Also another fun idea I want to try is to let the Claude design a new programming language, i.e. where the AI makes all the decisions and goal-settings and I just help it instead when it's stuck.