"Distributed Computing
Donate your computers computing power to a good cause such as
finding aliens or curing cancer. Look through this list of
distributed computing projects for Linux, and pick one that you
think is important.
"CCTV
Install ZoneMinder and connect a few webcams to watch around your
house. I was going to use a camera to check who's there when
somebody knocks on the door, but then I remembered I have a
peephole.
"Pimp Your Phone
Using Asterisk, you can do some awesome stuff such as music on hold
and voice mail. To get started, I think Systm episode 5 looks
useful, but it's about 3 years old, so it might be a little
outdated."