Only the 3 Mount and Blade games, with an upcoming 4th.
So how are the Mount&Blade games? I've never played that series before.
They are really nice. The best in my opinion and in the opinion of many others is M&B Warband, especially in the multiplayer. That's also a reason why they make a sequel of M&B Warband.
The problem I see is that you have to activate the games with a serial key. You can do it offline but you still have to do it.
It's the same when I asked some time ago for the release of Dominions 4 here on GOG where the activation method is the same and a blue one answered that they see it as DRM and thats the reason why it's not here. But I have no problem with that when you can activate games offline. GOG already has some games where you need a serial key to play in multiplayer but they don't want that you need a serial key to play in single player.