Choice of a PHP framework for LimeSurvey 2

=General=

=Criteria=

=Must-haves=
 * GPL compatible license
 * Support of Postgres/mySQL/MSSQL database systems
 * MVC model
 * Requires at least PHP 5.1

=Non-criteria=
 * ACL (because LimeSurvey provides it's own CRUD ACL)

=Other resources=
 * 1) List & comparison of web frameworks
 * 2) Best Lightweight PHP Frameworks of 2010
 * 3) Short comparison Yii - CI
 * 4) Short comparison Yii - CI #2
 * 5) Blog article "Yii vs CodeIgniter
 * 6) Short summary of PHP frameworks (Germany, 02-2011)
 * 7) Blog post "Yii vs CodeIgniter vs Simfony