Irmin
Irmin is a distributed database
.... Allows users to define custom merge functions and create event-driven workflows using a notification mechanism. Runs anywhere from Linux to web browsers and Xen unikernels. Allows the users to define custom merge functions, use in-memory transactions (to keep track of reads as well as writes) and to define event-driven workflows using a notification mechanism. You can use Irmin on top of your own storage layer.