I have recieved five invitations for the alpha of Freebase, the first five comments on this post with a valid e-mail adress will be invited.
Freebase is “a structured, searchable, writeable and editable database built by a community of contributors, and open to everyone”. Everyone are allowed to edit and add data and topics, categorized into domains, types and instances. Read more about it on the Freebase FAQ.
Freebase is like a more structured Wikipedia.
Freebase has a nice API for creating Freebase enabled applications. You can easily query and edit the Freebase for information using JSON.