I've got an old HP laptop running a pihole-alike, boinc, syncthing, and a webcam capture from my window: https://johnrockefeller.net/guelph-webcam.

In addition, I also host local files in a temporary way so other machines in my home network can pick them up easily with `php -s`.

Running a home server on an old laptop is very useful. If you're worried about power usage, just set the CPU to the lowest MHz like I did.

If you're doing it, please don't forget to look at boinc, because they need all the help they can get with computing power.