In the ongoing quest of the guys over on the Hardened-PHP project to help protect PHP installs from the evils of the internet, there's a new project in development that could help make even more PHP installations more secure - Suhosin.
Suhosin is an advanced protection system for PHP installations. It was designed to protect servers and users from known and unknown flaws in PHP applications and the PHP core. Suhosin comes in two independent parts, that can be used separately or in combination.
The first part is a small patch against the PHP core, that implements a few low-level protections against bufferoverflows or format string vulnerabilities and the second part is a powerful PHP extension that implements all the other protections.
There's already some information on the project posted on its homepage, but since it's still a beta preview of the code, the feature list and documentation isn't complete. If you'd like to check out this project in its early stages and see what it's all about, a great place to start is the current information including links to the downloads and how to get it set up on your install.