Do you know others frameworks like PEAR (http://pear.php.net) ? I want to use reusable PHP components without using the famous PEAR. I already use a framework (Zend Framework) and i want to use php components who doesn't exists in ZF like payment, encryption, math...
I don't really do that much php, but I've worked along side php developers for some time and I've heard comparisons between PEAR, SMARTY and Zend Framework all the time. I can't really tell you how much alike they are, but these are the ones I've heard about the most. I've also heard some saying they work with Cake PHP or Symfony, but not as many.
I also found two nice comparisons that might help, here and here. That's about all the help I can be. Good luck. :)
Check out EZ Components. It is a very loosly coupled set of libraries that I always see as sitting somewhere between something like PEAR and Zend Framework. Superbly coded and up to date, it is something to take a close look at.
As a Zend Framework fan myself I don't see why you don't extend Zend Framework based to your needs. I use a rather simple method by having a classes folder inside my application folder which you need to set up in bootstrap or load with Zend_Loader and there you can define your own logic or import different modules you're interested in ( phpClasses might be also very helpful).
You also can find a lot of helpers made by Zend Framework's community which might be helpful at any given time. If you like to go and strip off pieces of code from different sources you might also want to try to import some of the modules from other frameworks like Code Igniter or CakePhp into Zend Framework and that probably would be a fun and useful thing for you and if you'd like to share, maybe for all the community based around ZF
And I should warn you about Symfony (that evilpenguin wrote about), if you're willing to try it just don't forget it's the "laziest" of them all.