[jhasse]

F-Droid for Android: https://f-droid.org/

Also nearly any Linux package manager ;) (if they count as an "app store" for you)

[zokier]

I think the definition of "store" generally implies the ability to buy things, which neither F-Droid or package managers enable.

[jhasse]

You're right, I didn't think of that.

Isn't it possible to buy something in the Windows Store and login just for this one purchase? Note sure though, but I think I remember doing that with Windows 8.

[scholia]

Yes, you can. Just make sure you never use two different log ins from the same account on your PC ;-)