Montoya linked to the Zend Framework.
I’ve used various ZF components in projects before (most significantly, the email, search, and feed modules). The result every time has been either:
1) I had to fix or work around a ton of bugs to make it work. or 2) I eventually replaced it with a different library or my own version because the bugs were too severe.
If you ever browse the source, you’ll see why: it’s absolutely terrible. I’d be embarrassed to take credit for most of that code, and I certainly would never release it and suggest that people develop applications dependent on it.
Avoid the Zend Framework.