Microsoft Flight Simulator 2020
The Windows client reads position, altitude, heading, on-ground, and COM 1 through SimConnect when the sim is installed on your machine.
GuFlight ATC is a host that your sim client calls. It speaks a live pilot and controller environment through GuVoice for Microsoft Flight Simulator 2020, Microsoft Flight Simulator 2024, and X-Plane 11 and 12. ATC only. Clearances, taxi, tower, departure, and the other aircraft on the frequency.

The Windows client reads position, altitude, heading, on-ground, and COM 1 through SimConnect when the sim is installed on your machine.
The same SimConnect path. The client does not need the sim present on the GuFlight ATC host.
The client speaks X-Plane’s UDP data interface for position and COM, and reports other aircraft when the sim exposes them.
Less strict phraseology. ATC is patient, rephrases the instruction, and tells you what the call means.
Standard ATC. Runway, taxi, altitude, and clearance in the usual form. A partial readback is sent back to try again.
Real-world expectations. Shorter tolerance. A proper readback is required, and a wrong one is corrected.
The GuFlight ATC host speaks every transmission through GuVoice. Pilot and controller are different voices. Other traffic is spoken the same way.
The same ATC, with speech on your computer through the GuVoice processor. The host still runs the flight. You are not billed each month.