My 2 cents:
Simple, no domain required stuff:
- Pi-hole for self-hosted DNS: https://pi-hole.net/
- Navidrome for self-hosted music server: https://www.navidrome.org/ (best to pair this with an external portable HDD/SSD for music storage)
- Set up syncthing on it and use it for automatic file back-up: https://syncthing.net/ (that external HDD/SSD will come in handy again).
More advanced, should pair with a domain:
- Nextcloud for your own personal cloud/calendar/etc: https://nextcloud.com/ - it won't be blazing fast but it will work well, I had it running on a pi for a while.
- Simple web hosting - the pi is great for hosting low traffic stuff like blogs etc.