As well as being an acronym for Chronic Fatigue Syndrome, CFS is also a remarkable new flight simulator from Microsoft that recreates the look and feel of flying a fighter plane during world war two. The user can free fly exploring many European cites and terrain or engage in realistic missions and campaigns against the enemy, often flying in a squadron taking on fighters, bomber formations and numerous ground targets.
Although I don't like to sing the praises of Microsoft - this is easily the most enjoyable game/simulation I've bought in ages. The scenery is detailed, often stunning - though it does very occasionally make my slow P200/32MB stutter. I recently bought a Voodoo2 card to give extra smoothness.
Instrumentation and flight dynamics are faithfully recreated and the dogfights seem frightening realistic as you try to manoeuvre your aircraft craft to shoot off various parts of your opponents. Other planes seem to manoeuvre with real intelligence and the way panels and smoke fly from bagged opponents has to be seen to be believed.
Microsoft Combat Flight Simulator Official Site