Dave Grohl covered many bands, and played many alternate versions of his songs.
There are also a lot of side projects like Probot.

Acoustic/Alternate Versions

A320 (Acoustic)

Aurora (Acoustic)

Aurora (Live)

Ain't It The Life (Artist Direct)

Breakout (Artist Direct)

Come Back (Live)

Disenchanted Lullaby (Acoustic)

Everlong (Acoustic)

Learn To Fly (Acoustic)

My Hero (Live @ Craig Kilborn version)

My Hero (Common Acoustic version)

Times Like These (Acoustic Release)

Razor Of Mine (Live @ Tsunami Relief Benefit)