OuroKey.com is described as 'EASILY BUY AND SELL DIGITAL GOODS KEYS'. There are more than 25 alternatives to OuroKey.com, not only websites but also apps for a variety of platforms, including Windows, Mac, Linux and Android. The best alternative is GOG.com, which is free. Other great sites and apps similar to OuroKey.com are Origin (Free), Instant Gaming (Free), Green Man Gaming (Paid) and G2A (Free).
G2A is an online marketplace (akin to eBay) for video games on a wide variety of platforms such as Steam, uPlay, Origin, Xbox and PlayStation. Both G2A and community members sell a wide variety of games on G2A, at prices which tend to be significantly less then standard prices.
Marketplace to buy/sell game keys for a myriad of platforms including: Battle.net, EA Origin, Free2Play, GOG.COM, NCSoft, Nintendo, PlayStation 3, PlayStation 4, PlayStation Vita, Steam, Uplay, XBOX 360, XBOX ONE, and others.