The weirdest thing I have done in Emacs is using it to generate WAVE files, with a visual interface. The music loops, so you can keep playing with it. I've given talks about the package at !!Con 2021 and EmacsConf 2020.
Info about this at https://zck.org/bangbangcon2021. Video at https://www.youtube.com/watch?v=BeTDIrJeriI. Bonus: the presentation itself is done from within Emacs, in another library I wrote.