Sophisticated, lightweight & simple CMS, based on Silex.
Installation:
Create a new folder, and clone from github. Then use composer to get the Silex micro-framework and components:
git clone git://github.com/bobdenotter/bolt.git bolt
cd bolt
curl -s http://getcomposer.org/installer | php
php composer.phar install
And you're good to go.
More detailed instructions can be found in the Setup section in the documentation.