My favorite home lab setup was when I had an old (originally XP, switched it to Ubuntu) laptop and a couple of USB drives in the top drawer of a scavenged file cabinet. I cut a hole in the back for the wires and it never generated enough heat for airflow to be an issue. I hosted my personal website on it, including a webcam of my aquarium, hooked it up to my doorbell, XMPP, used it for document storage... anything I needed a server for. I switched to an old Mac Mini for NAS after I moved and haven't had much time to mess with it since.