The big idea
The giant minds behind boxee describe it as a social media center. Using boxee you can play unprotected videos and music and view images that are stored on your computer's hard drive or on devices on your local area network. Additionally, you can enjoy content from Internet sources such as Hulu, SHOUTcase, and Flickr. The "social" component is the friends you add (and who add you). Friends can see what they're watching and listening to, with the idea that if your buddy Marty had the good sense to watch the latest episode of The Daily Show on Comedy Central, maybe you should too.
In order to use boxee, you need an invite. And you can get that invite in one of two ways. You can visit and sign up for an invitation. As of today, that invitation will be slow in coming as there are loads of people who'd like access to boxee and the service is weeding through endless requests. The other way is to find someone who has a boxee account and ask them for an invitation. Currently, there's no limit to the number of people someone with an active account can invite.