How to act as an Air Traffic Controller using JoinFS.
Euroscope
I've created a tool that will display JoinFS aircraft on Euroscope.
I've called it ESJFS and for those that would like to try it, it can be found here.
**EDIT Jan 2021**
I've just updated ESJFS to V3, which now includes an updater.
I don't update it a lot but If a new version becomes available, you will be notified by the updater.
I've also tweeked a few things, although it looks and works the same as before.
To use it with JoinFS.
1. Start JoinFS
2. Start the ESJFS tool.
3. Start Euroscope and click Connection.
4. Select Connection Mode = Direct to VATSIM
5. RealName, Cerificate, and Password = ANYTHING you like.
6. Server = 127.0.0.1 or the word localhost.
7. Connect to VATSIM TickBox = Unticked.
Finally Click Connect!
A picture of the settings I use is below.

The tool will now also allow a connection directly to FSX/P3D or FSUIPC (And possibly XPUIPC).
If connecting this way any Aircraft that is in your SIM will be shown on Euroscope.
Handy if you don't want to use the default FSX radar or you use Xplane which doesn't come with a radar AFAIK.
DEFAULT FSX RADAR
To see JoinFS traffic on the default FSX radar you must start as an ATC in the following order.
1.Start your sim and set up a Tower in Freeflight mode.
2.Open JoinFS and in the settings menu tick Enable ATC Mode and input the ICAO code for the airport you will be controlling.
3.Run the JoinFS client and connect to the network with your friends.
But Roo how do I start the Tower in Freeflight mode?
I hear you say.
Yes there is no option to start the default FSX ATC Tower in Freeflight mode as there is in Multiplayer mode, but there is the option to load a saved flight.
So if you are in multiplayer mode as a Tower you can save this flight to use in Freeflight mode.
1. Start FSX and go to Local Network LAN and click sign in.
2. Click Host a session (bottom right).
3. Select Freeflight for the session Type, put anything you like in the other boxes and click next.
4. Select Air Traffic Controller in the role drop down box, Select the airport you want to control, the weather you would like and the Time of day.
5. Click SAVE and save the flight as KLAX Tower (replace KLAX with the airport you chose).
Complete steps 4 and 5 for every airport you would like to have quick access too when wanting to control.
6. Once all the airports you'd like are created, click back and sign out which should take you back to the main FSX login screen.
7. Select FreeFlight from the top left.
8. From the Free Flight screen select Load half way down the screen.
9. Select the Tower you would like to control at and click Fly Now.
FSX Will load you into the Tower view at the airport you chose.
If you have the AI aircraft enabled you will see them on the radar screen too.
I would advise turning AI traffic off when controlling in Freeflight mode.
I hope that helps anybody wanting to control aircraft using JoinFS and the ATC mode feature.