arr, it's the ardupirates!

Here are some links for the Ardupirates.  Arr! They've forked the arducopter code base and have some impressive demos regarding camera stabilization.  On their wiki they mention these features:

• Working Sparkfun Magnetometer
• GPS hold
• Altitude hold with Barometer and Sonar
• Automatic camera leveling plus an automatic camera trigger! 

Here's some links:

• Ardupirates RCG thread
• Google Codebase
• Ardupirates Wiki
• Ardupirates Configurator (supports multiple hardware platforms) 
• Ardupirates Installer