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Steam no longer supports Windows 7, 8, and 8.1
(www.neowin.net)
This is a most excellent place for technology news and articles.
There was a time when software didn’t need an entire browser engine to run. We used to call them native applications.
Although looking at how small the pre-Windows 10 customer base is I imagine Valve would have considered it not commercially viable to continue supporting however easy maintaining the codebase was.