Homestuck is the perfect crossover property because I can imagine Karkat piloting a mech and trying to win at a baking challenge with the same level of ineptitude and despair.

Floralmarsupial made a Fallout;New Vegas au that I haven't been able to stop thinking of (https://www.tumblr.com/floralmarsupial/189220241704/my-piece-for-the-ff-homestuck-zine-my-fallout?source=share) and there's a pokemon au that I adore (https://archiveofourown.org/works/1192437/chapters/2433105)