AppArmor

AppArmor is a least-privilege system for Linux which uses the Linux Security Modules interface. Every "armored" application has a profile which specifies the privileges the program requires to do it's job. It's not clear to me right now if this project is still maintained or not, as Novell was leading it, but has since bowed out by laying off the programmers it had on the project.

Tony Jones while giving an overview of AppArmor to the Linux Kernel Mailing List said:

AppArmor is *not* intended to protect every aspect of the system from
every other aspect of the system: the intended usage is that only a
small fraction of all programs on a Linux system will have AppArmor
profiles. Rather, AppArmor is intended to protect the system against a
particular threat.

Now, this isn't a true capabilities system in that the profiles use names, and are explicit, but it does help enforce least privilege, so it's a very strong step in the right direction.