SELinux roles provide something similar, as well. Unfortunately, only if using SELinux.
I'd really, really, really like to see the core roles stuff enter the mainstream POSIX/Linux interface. Not the full domain management stuff of SELinux, but just enough to control file access and do PID checks to see which process are running in which roles (while still allowing them to belong to a specific user).
You can _almost_ emulate roles using groups, newgrp, group passwords, and so on, except that a process can drop its groups.