Stumbleupon Review of : http://kohanaphp.com
Like (and originally based on) CodeIgniter, but with many more awesomes.
It removes some of the klunks and bumps (including the PHP 4 compatability), and, so far (I've semi-converted one CI project I was working on to use it), seems more elegant in terms of its fundamental approach. I particularly like the pimped-up benchmarking/profiler and stack trace for errors (with automatic dumps of any objects involved); cuts out a lot of the time between "WTF?" and "Oh, DOH!".
And now, to try plugging Zend into it, a la beyondcoding.com/2008/11/14/using-zend-framework-with-kohana/ [beyondcoding.com/2008/11/14/using-zend-framework-with-kohana/] for those jubbly API modules.