Yes -- there is "Over Flanders Fields". You can find out more about it here http://www.polovski.com/OFF.htm
It's a free download as a mod.
It's a WWI mod for MSCFS3 that completely transforms that WWII sim into WWI.
Technically it's not free since you have to have MSFS3 on your hard drive but I think you can get MSCFS3 for $25.00 at Amazon.com -- if you don't already have it. You might be able to find it in the el cheapo bin at your local game store.