Most children of the '90s (and the late '80s, for that matter) will have some exposure to Double Dragon, whether via playing the actual game, or seeing Fred Savage play it in Nintendo-promo vehicle The Wizard. Whatever the case, for those not exhausted by the Steam Sale, the game is currently free with every purchase on GOG this week.
The sidescrolling beat 'em up trilogy is probably best acquired in tandem with some of the drastic discounts GOG is offering this week: Homeworld: Deserts of Kharak is 66 percent off; The Witcher 3 is 50% off; and various Pillars of Eternity tiers are also heavily reduced. Go forth and idly purchase games you may never play.
Oh, and here's the Double Dragon Trilogy trailer if you want to know what's at stake. The offer ends on July 3.