GOG.com has kicked off its annual Summer sale, only this year it's doing things a bit differently, and the best bargains will go to those who are ready to throw down cash at a moment's notice.

The next 24 hours have been dubbed an "Adrenaline Rush" sale. During the course of this sale, four mystery games will appear on GOG.com at huge discounts with no prior warning and for a mere three hours each. At the same time, GOG.com will be giving away 100 vouchers for free games to those who can name all the games featured in short, 5-second vignettes posted to the GOG Twitter and Facebook accounts. Both of these unorthodox discounts are in addition to the standard daily sales and hourly flash sales that fans expect from GOG's promotions.

While we'd love to give you more info on GOG's plans, the site is playing things very coy. We have no idea when the aforementioned four games will appear, nor which games they might be. Much as it's playing right into the website's hands, the only way to keep proper tabs on the sale is to visit GOG.com throughout the day.
[Image: GOG.com]

This article was originally published on Joystiq.