We've now put our collection of open-source libraries out on bitbucket. You can find and browse the code here.
By putting the code on bitbucket, we hope to make it easier for us to work together with other people in the OCaml community. We're just starting (I just started telling people that we're ready to accept patches a few days ago), and we already have some improvements coming in.
We're still working out how the relationship with external contributors is going to work, but I'm very hopeful that this will hlep make Core a foundation suitable for lots of people outside of Jane Street to use for building their own applications.
If you're interested in contributing, join us on the mailing list.