Something like Bitbucket (of course much less feature-rich). It must be able to hold multiple repositories, and be private (i.e. if you don't login, it doesn't show you anything).
It should be able to run on a Linux server, and if it's also easy to setup (like phpMyAdmin) it would of course be better.
phpHgAdmin seems abandoned and doesn't even have a website, and the others I've seen mentioned don't look very promising. This is usually a sign that "it doesn't exists", but maybe I just didn't search well enough.