This link is for FSX mission editor, to enable you to design your own missions, in an easier way than the SDK shipped with FSX Deluxe

FSHostSpy is a free program for finding FS2002, FS2004, and FSX multiplayer games on FSHost servers. It shows a list of FSHost servers currently online, as well as each game's session details, player names, aircraft, altitude, heading, speed, flight plans, and all the other details you want to know before joining a game.

If you want to connect your FSX to an FSHost session, you need this. If you're using FS2002 or FS2004, it can already connect to FSHost and you don't need this. If you're only hosting with FSHost, it already supports FSX and you don't need this.