To elaborate the Abyss is a gaming platform that uses a cryptocurrency they call the Abyss Token (ABYSS) for payment. Hence

Coindesk claims developers could add The Abyss’s payment solutions to games built with the Unreal Engine. Thus, The Abyss and the Unreal Engine could make it easy for developers to add cryptocurrency payment to games.

The difference between Steem and the Abyss is that they design the Abyss for massive multi-player online (MMO) games. In contrast, Steem is available to a wide variety of creators including writers, podcasters, bloggers, and moviemakers.