It can be used to perform SQL queries about the Git history and about the Universal AST of the code itself. gitbase is being built to work on top of any number of git repositories.
The emphasis here is on querying a bunch of repositories at once, not digging deep in to the history of a single repo. It uses MySQL's wire protocol to communicate, so it can be accessed by any compatible client or library. gitbase is still in early alpha, but they're working hard to improve it quickly.