User Manage is a compact suite that can easily be used in any PHP script. We modeled it like a puzzle: there is the "core" that handles basic authentication, and then there are other modules that handle utility functions (e.g. a database handler that help top-level modules like the permissions handler).
With User Manage, developers can build applications with the standard user authentication complete, and focus on the program's actual purpose.
IMPORTANT NOTE: The files listed at phpclasses.org are out dated. Visit http://usermanage.sf.net/ for the most updated versions.