zAlternator allows you to sync your Zune with software other than the Zune software like Windows Media Player, iTunes, Winamp, or Media Monkey. You can read more about zAlternator at this link.
And here is a description of the application from it’s homepage:
“Finally, a release candidate of zAlternator is here! Yay! zAlternator is a program that will allow the Zune to be picked up and synced with programs other than the Zune program. It has been fully tested and proven to allow the Zune to be picked up and synced with the Zune program (duh), Windows Media Player 11, Winamp, and MediaMonkey. I have been unable to fully test the iTunes side of the program, but hopefully it should work.”