NOTE: If you have not used IF for a while you might need to re-register due to changes in Windows security measures. Make sure to have the latest version of Ideal Flight before registering or it will have to re-register when you do eventually update.
7/8/2018:
Latest updated IF versions: Preview 11
Ideal Flight Professional P3D v4
Ideal Flight 10 Professional P3D v3
Ideal Flight 10 Special Edition
Ideal Flight 10 Original
Note: The IF link/menu item that checks for the latest version only refers to releases on the main download page.