Syncopation

Although you can use iTunes to remotely access any multimedia library on a computer connected to the same local network, you might be interested in keeping the exact same library on all your computers.

Syncopation is an application for Mac that lets you sync your iTunes multimedia library between different Mac computers. It works with music, podcasts, movies, and TV shows.

It can find and recognize multimedia files present on one of your computers but not on the others, and then sync the files to match the libraries.

Any changes that you make to one iTunes library will be reflected on the rest of them. This includes the songs you get through the iTunes Store, the CDs you import, etc. You can also create a list of files you don't want to be synced, for whatever reason.