Freebase is “an open, shared database of the world’s knowledge“.
From the Freebase FAQ:
1. What is Freebase?
Freebase is a uniquely structured database that you can easily search, add to and edit; you can also use the data in it to power your own projects. It’s a data commons in the way that a public square is a land commons—available to anyone to use.
Example: Search Freebase.com for “open access”.