Call for VTOL test pilots! The PX4 standard firmware (master branch, downloadable via QGroundControl) supports first VTOL vehicle (duo-rotor, tail sitter). This video demonstrates the transition from hover - fixed wing - hover. Contact: http://px4.io/vtol.
Additional vehicles are currently in testing, including a BirdsEyeView FireFly Y6 (tilt rotor) and a Quadshot (quad tail sitter). The main benefit during initial bring-up of VTOL support of the TBS Caipirinha is its small size and high operational safety, combined with the inherent ruggedness of a flying wing airframe.
As the PX4 flight stack (running with the PX4 middleware on Pixhawk) is unified platform without separate multicopter or plane codebases and using the same command & control (arming, logging, safety) state machines and mission management for all platforms, its perfectly suited for VTOL development. Adding VTOLs didn't mean to introduce a new vehicle category, rather, it mostly meant adding a new mixer, a VTOL transition controller and some minor tweaks.
Note these are initial results leveraging existing multicopter and fixed wing controllers spiced with a VTOL transition controller - the dev team is meanwhile experimenting with model predictive controllers. But even this initial baseline implementation works quite well and is ready for some flying.