Why care about another PHP framework? especially one that's actually called Yet Another Framework? Because Yaf isn't just a framework. It's a PHP extension (listed on PECL), so it's written in C -- so it's very, very fast. How fast? Here's a benchmark (requests/sec).

The only framework (of the list he compared) that came in faster was MicroMVC and that's not as full-featured as the Yaf functionality is. Disregarding that, it has a huge requests/second difference between even the next on the list, CodeIgniter.