What are some cool projects that I can do with a 1st gen Raspberry Pi?

Take a look at the Linuxserver Docker images. They curate a huge list of self hosted apps that is great to browse and look for ideas. You don’t need to run Docker and use their images - I’m just suggesting review their list of apps they support to get some ideas of what’s out there.

That Pi is too old to handle any media tasks (like running a Jellyfin server), but for any low intensity duties it’s still perfectly usable.