DCS WorldThe abbreviation DCS stands for Digital Combat Simulator.  DCS World is a digital battlefield with a focus on military flight simulation.  The manufacturer is the Russian team of Eagle Dynamics.  The DCS World is an offshoot of the professional military simulation TBS (TheBattleSim), which is programmed by Eagle Dynamics as a simulation platform for various military personnel according to individual needs and is the actual economic background for the development team.  

DCS World provides the basic framework of this flight simulation kit for everyone free of charge.  It contains a large modern Caucasus map, two aircraft (Su-25T and TF-51D), the mission editor and a number of modern AI objects for creating (training) missions and campaigns.  

Additional airplanes, helicopters, tanks, maps, AI objects etc. are offered as additional modules for a fee.  These modules integrate seamlessly into DCS World.  Thus it is possible that an owner of the module A-10C can play together with a friendly player, who e.g. owns only the module F5E-Tiger, on a multiplayer server.  The basic module DCS-World is a prerequisite and must be installed first.  

Some of the paid add-on modules were created by Eagle Dynamics, others are offered by third parties.  All modules must comply with Eagle Dynamics quality guidelines and include clickable cockpit instruments (exception: Flaming Cliffs 3 models) and full (6 Degrees of Freedom) TrackIR support.