Currently in alpha, Boxee is a free cross-platform media center service that allows you to view both local (HDD, DVD etc.) and Web-based content in a TV-like manner. You're able to access content from a wide variety of sites, including BBC iPlayer, Joost, Last.fm, ABC, CNN, CBS, Comedy Central, MTV, Netflix, YouTube and so many others. It supported NBC's Hulu but was asked to remove the function back in February and the two have yet to establish terms.
Boxee incorporates a dense layer of social networking as well. You can follow the activity of another user, add them as a friend and publicly rate and recommend content. Your media activity can be exported to other popular social networking services like FriendFeed, Twitter, and Tumblr. It also features support for Python widget scripts to expand on its functionality via community written plug-ins and add-ons.
Naturally, a service of this magnitude which embraces free Web content poses a threat to big names in the TV industry - cable and satellite companies are still heavily reliant on hefty monthly fees. If you've seen Boxee in action, leave us your impressions in the comments.