An open source engine clone of Age of Empires II
I wish someone would clone Cossacks.I've been playing it since 2002 and keep an XP box specifically to play  it on. After all these years I still haven't gotten bored of the game and probably play it 2-3 hours a week or more on average.I don't know if this means it's a really good game or I'm just a boring person. But it beats AoE all over in my opinion. I've tried a lot of other games, played them for a bit and forgotten about them. But not Cossacks. I just wish they had kept the series going.