I don’t expect much but I found an old pi I bought probably 2016(may of been 2017). It was supposed to be a pi-hole but was never able to get the dns forwarding to work on my modem. It still works but wanted to somehow convert it to a regular distro(it’s based on a micro-SD and I don’t have any more microsd readers). I wanted to set it up as a basic system I could ssh into a terminal. Not expecting anything fancy or even graphic based. A lot of stuff I want to learn/practice “work” on windows but are native to Linux, like vim/neovim nmap gcc etc. Is this feasible? Am I under estimating what’s possible with it?
XMPP server, do some decentralised communication under your control. It will federate to other servers, allowing you to speak to other people and join public chats. An old Raspberry Pi should easily be able to server 100 or 200 users. Try Prosody for that or Snikket if you prefer containers and everything working out of the box.
You could also use it as a NAS, if you don’t need a fast NAS. It will probably be enough to stream HD media using VLC on a cheap Android TV device/dongle.