There's a bunch of new sales on GoG as part of their big sale. Also of note is that a bunch of new games have been added to GoG Connect, meaning if you own the game on Steam, you can get a DRM Free GoG version as well. The biggest addition is Metro 2033 Redux.
https://www.gog.com/news/make_way_for_the_monstrous_fall_sale
The two games I got through GOG Connect were Metro 2033 Redux and The Witcher 2. I'm surprised Witcher 2 and 3 weren't included in the first run like Witcher 1 was.