Security/2

Security/2 is a multi-user system for OS/2. It provides controlled access to files, drives, drivers and other OS/2 stuff, based on access control list for each user.

Structure
Security/2 has modular structure, can be easily extended and provides an API for developers to enable their applications be multi-user.

Using Security/2
Most of the Security/2 utilities are open sourced, that provides additional help for developers.