Ok, if you enjoy music, you gotta check this out ->
MidiJam: http://www.gamesbyscott.com/midijam.htm
Play a midi, you see the 3D instruments (~180 available and growing) actually being played in real time on a stage and you control the “camera”, close up, overhead, pan. Almost all instruments shown with actual notes played, i.e., the specific string and fret on guitars, with the strings vibrating, the correct piano keys are played, horns, every kind of drum, some instruments I don't even recognize. See the screen shots on page referenced above. Just instruments, no people except hands on bongos and singers up to a full choir shown behind the stage when voices are part of the music. Comes loaded with a bunch of midi songs - pop to classic. And/or you can import midis, or write your own song in today’s download, MagicScore, and watch it played in MidiJam.
Totally free. In active development, adding more instruments, controls. Serious resource hog, but you’re watching a whole freakin’ orchestra playing... Vivaldi for example. So max out your cooling fans, drop your machine on a big block of ice, sit back, open a cold one and enjoy the concert.
If you write music, especially for guitar, check out "TuxGuitar: A Multitrack Tablature Editor and Player" at: http://www.tuxguitar.com.ar/ Totally free. Open source as well, I believe.
You can compose music using:
* Tablature editor
* Score Viewer
* Multitrack display
* Autoscroll while playing
* Note duration management
* Various effects (bend, slide, vibrato, hammer-on/pull-off)
* Support for triplets (5,6,7,9,10,11,12)
* Repeat open and close
* Time signature management
* Tempo management
* Imports and exports gp3,gp4 and gp5 files
Useful for many instruments, but designed specifically for writing guitar tab.