new user, feed data to two websites

I'm a new user, looking to set up my receiver (FlightAware Pro Stick Plus). I'm expecting to run it on a Raspberry Pi. Is there a way to feed the data to both OpenSky and FlightAware from the single receiver?

Welcome to the community! There shouldn't be a problem installing both the FlightAware and the OpenSky feeder on the same Raspberry Pi. As long as your setup is based on a Debian system, you should be able to simply "add" the OpenSky feeder by installing it according to these instructions:
opensky-network.org/community/projects/30-dump1090-feeder

Hi -

I have done that exactly: I started off with installing dump1090 (on the RPi) and then hooked it up to three different clients: OpenSky, Flightware and Flightradar24. It works like a charm.