Windows IIS probably from around the time of windows 8 so maybe 2012. Probably running on either windows server 2012 (like exchange, an active directory domain controller, or if you are unlucky sharepoint) or some weirdly configured appliance running windows 8 ish enterprise.
I remember at least one indie dev saying that they would prefer you pirate the game instead of using key resellers as they tend to cost the devs lots of time and money dealing with credit card fraud.