We recently created an audio server. Spotify and the like are nice, but we found that there was a large amount of music we like which wasn't on those platforms (or if it was, it wasn't the version we liked, etc).

One cheap Raspberry Pi 3 and large reliable usb storage later and we have our own streaming service. The option to stream is only available locally (didn't want it discoverable on the internet at large).

On the note of you having children, and not knowing their age, I would also suggest a Minecraft server? No idea on what it actually takes to host one of them though.