I've been working on this since over a year now and am happy with the results achieved, so why not brag about it :).
The project originated from ArduCopter after I bought one and started playing with it. I've rewritten all of the functional code in an object-oriented fashion. I reused the driver part of ArduCopter code, though. I'm using APM1 as low-level autopilot and iEi PM-PV-D5251 Single Board Computer (SBC) with 2GB RAM and 32GB flash for higher level tasks performed onboard. The SBC runs Linux (Ubuntu 10.04) and Robot Operating System (ROS). I used rosserial for APM<->ROS communication.
I'm planning to release the code I've been using around October as LGPL and was wondering if there is interest for such a project in the community. The platform is aimed at research entities and hobbyists. The platform I'm flying costed less than 1000USD (without laser scanner visible on images below). There is also an option to replace the SBC I'm using with a PandaBoard or BeagleBoard for lower cost (and lower performance, though). Other platforms (like fit-PC without casing) would fit too, of course.
The code is not compatible with ArduCopter any more nor I think there is need for it to be, but I'm open for all good ideas. It only supports APM1, but I think migrating to APM2 shouldn't be very hard.
Any friendly questions invited, I'm curious of your opinion. I'm planning to record a promo-video in one or two months with the quadrotor performing indoor SLAM, just don't have time for it now.