Hi John - welcome back! I see you've lost an N from your username - adopting a sleeker styling!
The Commstation is the new AirNav box to replace the original - capable of doing multilateration at last. I believe it's still officially in Beta testing at the moment, so there hasn't been a formal announcement. It explains why we are now seeing non-ADS-B aircraft like Embraers and Dash-8s on the network, though at the moment they seem to hover around for ages - I hope that's being worked on.
As to these dongles, they are low-cost ADS-B receivers - more than that, I haven't a clue - I'm sure somebody will do a beginners' guide for us one day.
Stay tuned!