The GOG Big Winter Sale has started and ends on December 13th. There’s 500+ titles on sale for up to 90% off.
There are bundle deals and mystery games on sale for $3. You also get a free copy of Divine Divinity if you spend $5+ and Blackguards Special Edition if you spend $50+.
The first set of deals runs for 48 hours as a launch special. After that deals and bundles rotate every 24 hours.