For simple key/value storage, you might like to consider [Berkeley DB](http://en.wikipedia.org/wiki/Berkeley_DB), though I would not think Git would be the best for 'version control'. You can use [Ruby bindings](http://stackoverflow.com/questions/577447/how-to-retrieve-all-the-records-from-a-berkeley-db-in-ruby) with BDB.

Since your edit, I'm left wondering If you want an open-source implementation of something like Amazon S3