Yes, GOG had a sale only last week, but now the site is running another sale (opens in new tab). And this time, they're calling it 'The Big Deal Sale'. Why is it a big deal? Because in addition to there being upwards of 200 items on sale, there will apparently be something "absolutely, definitely, positively special" for everyone who visits the site on Tuesday (or Wednesday in Australia).
What's on sale? Nex Machina is available with a 45 percent discount, while Her Story, Banished and Shadowrun: Hong Kong are all available for 75 percent off. Other massive discounts include Oxenfree (75 percent), Satellite Reign (85 percent), Firewatch (55 percent) and The Witness (60 percent).
There's plenty more where these came from, and you've got until September 25 to peruse the list. As for what tomorrow's "absolutely, definitely, positively special" thing, I've got no idea what it is, but I'd guess it's a free game of some variety.