FrSky is a pretty solid and reliable RC control system. It has an open telemetry protocol which can integrate in with several different flight controllers.
There are three generations of products:
- Non-telemetry V-series
- Telemetry D-series
- New S.Port telemetry X-series
FrSky also makes receivers compatible with other protocols like Futaba FASST, not to be confused with their own systems.