This is Web Apps. Web Apps, by and large, shouldn't care about what a user's underlying operating system is. Still, we have a bunch of questions that are tagged with operating system names.
- linux x15
- windows x20
- windows-7 x7
- osx x15
- mac x23 is technically hardware, but I think it applies here
- ios x9
- iphone x36 is technically hardware, but I think it applies here
- android x29
Now maybe some of these are correctly applied. (I don't have an example of what such a use might be at the moment.) If so, then leave the tag.
In most cases, though, the tag was used to describe the Asker's system, not to describe what their question was actually about. In those cases the tag should be removed.
As always with any clean up project, don't just fix this issue. If you're going to edit, edit everything that's wrong with the post. Fix grammar/spelling, fix formatting, remove greetings, remove "thanks", remove signatures, etc. And limit yourself to just a few at a time so the front page doesn't get overloaded.
Of course, if the question should be closed, then vote/flag as appropriate. (Probably shouldn't bother editing.)