We've got an experimental IMAP server using Irmin as a maildir-replacement backend, to give us e-mail provenance and undo for when mass moves go horribly wrong. It's not quite ready for open-sourcing yet, but should be over the summer. I'm switching my personal e-mail over to it soon gulp
They are different design philosophies: Irmin is closer to "Sqlite-with-Git-instead-of-SQL", since it's just an OCaml library that lets you build graph-based datastructures that are persisted into memory or Git. Higher-level datastructures are built in the usual OCaml style on top of it.
You could build a Camlistore-like service on top of Irmin, but this design/eval hasn't happened yet to my knowledge. It's on the TODO list for Irmin applications -- while I really like Camlistore, I do also want finer control over routing of blobs in a content-addressed network to manage the physical placement of my personal data.
Another interesting aspect of Irmin is that the backend blob stores are also just another functor. In addition to the existing memory/HTTP-REST/Git backends, we've sketched out the design for a convergent-encrypted backend store as well. Other backends such as existing k/v stores like LevelDB or Arakoon shouldn't be difficult, and patches are welcome.
