Mini OSD for the Pixhawk Flight Controller has a companion OSD board called MinimOSD. It reads all the MAV Link data in the APM telemetry stream and overlays it on the video stream if you're using an onboard camera and wireless video transmitter. This is useful if you're flying in First Person View (FPV) mode or don't want to use a laptop in the field to see your telemetry data in the Mission Planner.