Mirroring/flipping a display (context of a #DIY #HUD display).
#Windows: 54,99 USD software
#iOS: I can't afford it.
#HDMI: buy this 599 USD black box or hack something form chinesium. And no HDCP for you, just out of spite.
#Android: no, unless a given app is especially written for it. Otherwise “no”.
#Linux: `xrandr --output $DISPLAY --reflect $how`