Conceptually it's a sql proxy that decides how to maximally encrypt data based on the operations that are required. It can then weaken and re-encrypt portions of the data on the fly so that more powerful operations can be performed.
You can chain the encryption to the users login to to prevent cross user leakage.
This model allows you to have a database that is protected from adversary who have access to the database.
The encryption techniques include a partially Homomorphic scheme and other non-homomorphic schemes.
I believe that the team behind it seem to have moved on to a startup using similar technology. The code is not being actively maintained anymore. I was able to build it successfully on Ubuntu 12.04 with Bison 2.x(The code requires a mysql build which chokes on BISON 3).
They claim only a ~15%-25% performance hit although I've not yet be able to replicate that myself yet.