Are you too poor to pay for a $75-100 game and guitar mix?
Look no further, use your keyboard as a guitar and play:
Frets on Fire!
Well, now that that's out of the way,
It's pretty much a Guitar Hero rip-off, but fun non-the-less
Some in game pics:
(Not mine, I'm too lazy to get my own, these are off the internet)
This is how you hold your keyboard:
F1-F5 keys are the fret buttons, and enter or shift is the pick.
I have a laptop, so I had to scrounge up my old wireless keyboard, or else it wouldn't be as fun!
Link to site:
http://fretsonfire.sourceforge.net/