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Like Amazon's other gaming acquisitions, GameSpark isn't a game developer - instead, the company provides what it describes as "the ultimate backend development platform for game developers." In so many words, GameSpark provides a framework for the creation of games.
It stands to reason that, if GameSpark was indeed purchased, Amazon will now offer the services that GameSpark did at one point - presumably through its Amazon Lumberyard program.
Lumberyard, which was introduced back in February 2016, is an all-in-one game development engine. In English, that means it can be used to create games that can then be supported by Amazon's internet hosting services (AWS) and Amazon's game streaming service (Twitch). It's a kind of "closed ecosystem" approach to game development that encourages any developers using the service to also use Amazon's other services to support their games.
GameSpark offers services like leaderboards and microtransactions, potentially offering additional services to Amazon's Lumberyard game development service. For its part, Amazon hasn't officially announced the acquisition, nor did it respond to request for comment as of publishing.