You could use Vassal, but its mighty intensive.
I considered using it for our game against Meanfcker and his friends.
Youd use the screenshot as the "game board", it has network options, and could function as a virtual "war room" where you could move pieces around, chat, draw lines, write on the map, place objects, etc.
Itd take some time to set up, but for games that go on for months and months, it could be a weekly "meeting", where the team gets around and formulates plans. I know people have used it for very large multiple player TOAW3 scenarios in just that way.