A PHP < 5.3 compatible yet usable authentication framework, it was born out of the necessity of having a generally solid authentication framework while at the same time having to work with creaky old PHP 5.2.
Originally built for a friend's upcoming website when I learned his hosting company doesn't quite get it's no longer 2006, it's flexible enough to develop a number of authentication schemes while strict enough to avoid polluting the system with garbage. It's because of this that I've decided to integrate it with my other website-building tools and called it Neutron/auth (Neutron being the internal name for all this tools)
Proper documentation is upcoming, but there's a repo with a demo you can poke around which will hopefully clear some concepts of how to work with the toolset.
The stablest code is in the master branch, while the development branch is in kind of constant influx.