One of the new columns in the Task Manager is "Operating system context". Most things running or at "Windows 8" level, but some third party apps are at "Windows 7" but the most disturbing one is Microsoft's own Messenger (desktop version) running at "Windows Vista" context level... and I have no idea what that actually means. I thought it may have something to do with compatibility level, but nope.

So what does "Operating system context" mean?

It indicates the compatibility level indicated by the application's manifest, if any.

An EXE without <compatibility> section shows "Windows Vista" as the default.

Note that you can see the "Operating System Context" in the CPU tab of RESMON as well even on Windows 7.