This is not an add-on, but the basic package itself. Written by Hardy Heinlin, PS1 now has officially sold out and you can only get it second-hand. There still is a Aerowinx web site with several interesting downloads.
ACARS is the message exchange system between planes and ground stations. ACARS carries company messages, operational information, and air traffic control communications. ACARS is not strictly a PS1 add-on, as it can also be used in combination with other flight simulators, or even without any, as ground station. Author: Jeroen Hoppenbrouwers. Web site: http://www.hoppie.nl/acars/ .
The Broker is the telephone exchange of the system built around PS1. You need the Broker as soon as you want to run anything else besides PS1 itself. Author: Jeroen Hoppenbrouwers. Web site: http://www.hoppie.nl/broker/ .
The Dual MCDU package offers PS1 users limited access to two independent FMS interfaces. Great to display on the side of the handling pilot. Author: Jeroen Hoppenbrouwers . Web site: http://www.hoppie.nl/dualmcdu/ .
Flight Crew is a simple environment noise generator. It reacts on events coming from PS1 to play WAV files. Author: Jeroen Hoppenbrouwers. Web site: http://www.hoppie.nl/flcrew/ .
The Flight Data Recorder writes a timed log of all things happening in the PS1 world to disk. This includes all plane motion, so a slaved MSFS scenery generator will follow nicely when played back. It is handy to record whole flights at the data level instead of as a video. Author: Jeroen Hoppenbrouwers. Web site: http://www.hoppie.nl/fdr/ .
The GoFlight Bridge is an interface between GoFlight hardware modules and PS1. It supports FG45/46 transponder panels, GF166 radios, TQ6 throttle quadrants, and T8, P8 panels for pedestal/overhead control. Author: Jeroen Hoppenbrouwers. Web site: http://www.hoppie.nl/gfbridge/ .
The 747 Inter-Process Communicator opens up PS1 for access by the outside world. It extends PS1 functionality chiefly by enabling network connectivity. In a sense, it is for PS1 what FSUIPC is for the Microsoft flight simulator. Author is Ivan Ngeow <rimb1991(at)yahoo(dot)com>. Web site is http://open744.sourceforge.net/747ipc.html .
For most people, the fully automated all-in-one 747IPC Installer is the obvious choice to acquire 747IPC.
Open744 is a wrapper for the Aerowinx 744 Precision Simulator (PS1) that lets you run the sim under Linux or FreeBSD without a DOS emulator. Author is Ivan Ngeow <rimb1991(at)yahoo(dot)com>. Web site: http://open744.sourceforge.net/
The overhead panel enables total remote control over PS1's OverHead Panel. It includes some extra goodies for operational comfort, such as PS1's voice checklists handling. The OHP also features MCP, EFIS, EICAS control, remote actions on all PS1 systems (apart from flight controls), control over PS1's CDU, and flight parameters monitoring. It requires PS1OPF v0.6.4, 747IPC v3.1 and the Broker. Author: Pierre Theillere. Web site: http://perso.numericable.com/pierre.theillere/cockpit.html .