Assembla.com is a code-hosting/project-management site similar to BeanstalkApp (which RB supports).
I don't know exactly how SCM plugins need to be implemented, but I'm not sure whether Assembla can be easily supported as I haven't found an API for git so far (though the API does let you manage SSH keys for a project).
http://api-doc.assembla.com/
Individual git commits are available through a web interface, though only with an HTML diff viewer. URLs are like this:
https://www.assembla.com/code/<project-name>/<git-repo-ID>/changesets/<sha1>
(Projects can have multiple git repos, so <git-repo-ID> should be "git", "git-2", "git-3" etc.)
Individual file diffs within a commit are also available, but again only as HTML, with the URL format:
https://www.assembla.com/code/<project-name>/<git-repo-ID>/node/diff/<old-sha1>/<new-sha1>/path/to/changed-file.foo