Is gog going to distribute the third part?

Not that I'm GOG staff or anything like that, but I would guess "No," because UFO: Afterlight only came out in 2007. It's not exactly "Old" yet. I think the youngest game available on this site at the moment is Earth 2160 which came out in November 2005, so it's probably best not to hope too hard for any game that was released after that time.

The Driver game that GOG sell was released in the summer of 2007 so that isn't exactly old either. It is, however, a flawed game that Ubisoft probably are desperate to shift a few extra copies of, so that's why it's offered here. Afterlight probably still has a fair bit of mileage in it before the publisher will feel like selling it DRM free. I hope at some stage it is offered here. It's the only one I'm yet to play and although I'm not massively impressed with the first 2 games, there is some entertainment to be had from them.

Collie, you definitely should try Afterlight according to my friend who played through all three. It's a very interesting shift from the first two games as you're now trying to colonize and terraform mars at the same time as you're trying to defeat your enemies. It's an interesting combination of different forms of strategy. Hopefully they'll add it up here, I'm not buying the two first, I'm only interested in the third.

But when you liked Afterlight, you want to give a try to Aftershock. And as you will like Aftershock (you may even finally prefer it!), you will want to give a try to Aftermath...

Afterlight is second best to me, Aftershock is best gameplay overall to me in the end. Afterlight is still good but just different enough to put me off. Too much RPG added to the last one.