Run a web-server, a file-server, and/or a video-server. You can make it into a retro-console, or a portible computer. It depends on how much effort you want to put into it!

Install RetroPie and turn it into a game console. It’s got plenty of power to emulate a lot of older consoles. You can even connect some game controllers from old consoles to the GPIO pins.

Make a computer for kids by installing PrimTux or other kid oriented distro.

You could run Pi-hole

Cups print server, pi hole