It is not unused. Idle CPU/RAM/etc will be in low power mode and not consuming nearly as much power as doing actual work.<p>It is not a free lunch!<p>People like BOINC like to say otherwise. They are wrong.
boinc.berkeley.edu/<p>The BOINC daemon can be run headless and unattended (while logged out).<p>You can also create your own projects/initiatives to leverage the BOINC community.