Paparazzi is not so much a single autopilot as an integrated open source UAV development environment, with a variety of hardware and software elements.
There is some AVR-based hardware (obsolete), mature LPC-based family and a (bleeding-edge) STM32-based autopilot hardware.
Paparazzi autopilots can be configured to work with thermopile, IMU or AHRS stabilization. There are paparazzi hardware designs for these, and various commercial and other open source alternatives are also supported.
Paparazzi includes software for ground control, flight planning and simulation, as well as a variety of associated tools. And the actual autopilot software, of course.
The "Paparazzi Center" tool is used to build, manage and deploy UAS software, including:
- mission-specific ground control software
- simulator (HITL or not)
- communication links
- video recorders, speach dispatchers, plotters and loggers, etc etc.
Paparazzi center manages "sessions", collections of UAS software configured to be run together. It also manages a configuration-driven build system incorporating many different modules/subsystems to support different sensors, payloads and mission features. While there are some basic reference implementations, this sophistication comes at the cost of complexity, it's definitely not a "plug and play" solution.
Paparazzi is ideal for developers that want to integrate some novel feature into a complete working system, then make that feature available as a module for other UAS developers (e.g. academic and scientific users). It presents a potentially higher barrier to entry than some other autopilot projects, and is not as popular with hobbyists (even though the costs are comparable). There is also a risk that, once over the learning curve, users find themselves leaning over the parapet sneering ""we aaaaaready gotta-one" to the other autopilot projects (or passing African swallows).