The Linux-Privs project is an effort to implement a POSIX.1e (formerly POSIX 6) security model under Linux.
At the heart of the changes to the Linux kernel from the historical model is the separation of identity and privilege. Historically, root (UID=0) was all powerful and other users (UID!=0) had power that was limited to that associated with their identity and their group memberships.
The Linux-Privs scheme is to implement a set of independent capabilities that can be given to any user. In point of fact, the capabilities are associated with applications and can only be used within the confines of the functionality of such applications. In this way individual capabilities can be restricted to a trusted set of applications. Typically, the user will have to authenticate himself to such an applciation before it will perform its privileged task.
This new scheme for system privilege lends itself well to restricting privileged access to the system and reduces the risk of intruders or poorly written applications running amok on the system.