Groups is a WordPress plugin that provides group-based user membership management, group-based capabilities and content access control. It integrates standard WordPress capabilities and application-specific capabilities along with an extensive API.
libcap implements the user-space interfaces to the POSIX 1003.1e capabilities available in Linux kernels. These capabilities are a partitioning of the all powerful root privilege into a set of distinct privileges.
Linux PAM modules that implements a mapping of users and group to roles with POSIX draft capability bits set.
Only tested against Linux 2.4.18 (at this time). Updates for testing with 2.6+ in progress...