Looks promising! I've actually been developing my own Sinatra clone in PHP5. I've called it "Slim". It has RESTful GET, POST, PUT, DELETE routing. It has before and after callbacks. It has Page Not Found handling, halting, helpers to set custom response codes, and easy-to-extend templating (use Smarty, Twig, or whatever you want). See more at:
Documentation: http://slim.joshlockhart.com/
GitHub (with Download): http://github.com/codeguy/Slim
Still very much a work in progress, but thought I'd go ahead and get the word out.
Enjoy! Josh