You can do that with Gitorious and many other web front-end for git and/or other vcs (if you need a web front end at all, which is not really clear, and git-web is sufficient if you just need an easy way to link to some commits or file in your source tree).

What would be nice on these open source web front-end for git is decentralized pull/merge requests, I don't know if there is one which does that yet (like you can follow someone with another Status.net install on identi.ca for instance, you could issue pull/merge requests from any "nodes"). Also, this would kind of make a lot of sense for a dvcs.