[
OT]that arrow near the minimize button in your screenshot... where does that come from?
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OT]
This is from TeamViewer, a remote control software.
Ultramon would be useful for me, because it allows to move the window from one monitor to another if my second or third monitor is off. So I can fetch the window from there. I just have to disable the additional taskbar in the setup, because otherwise I can't reach these windows.
Unfortunately there is no standard for additional buttons, so they interfere with teamviewer's at the same position... (But all are useable though.)