cmd.exe and calc.exe from ReactOS can be used since ReactOS aims to be fully binary compatible. They look a bit bad though.
Or this is a good opportunity to use tools not built into the OS or write own replacements. It's a bit silly to have calc program dictated by the OS version.
I wonder if you could get into legal trouble if you start to re-distribute calc.exe from older Windows version, as a free download. Probably yes, but it would look so ridiculous if MS lawyers would go after a random person doing that.
The thing is that your Windows 8/7/Vista/XP versions of calc don't even run on Windows 10. The only thing you can run is the Calculator Plus that was released for XP. Of course Microsoft did remove the download for that one.
Not him, but I would have stayed on 8.1 too if it weren't for processor support. The only annoying thing about it is the start menu, which i only use for maybe 10sec/month. It's faster than win7 and has a bunch of features I would miss, and compared to 10 it's not as bloated with non-win32 apps with less functionality for everything, tracking that you can turn off, and all the other win10 stuff you've heard already.