Oxygen is a small and light framework. It is currently in active development. Work is underway on a new version that includes session, user agent, (better) MySQLi support and form helper/classes. You can still define your own methods to use in your app, and all of PHP's functions are available.

Clone from GitHub:

http://github.com/snicol/oxygen

Install Oxygen by uploading, then changing the info in /system/config for both system and db (if you're not using a db, you don't need to). You can then create a masterpiece! Check the documentations here.

Currently in RC3a, version 0.1 being developed.