Use a front surface mirror to create a teleprompter PC
An optical mirror can be placed at a 45 degree angle next to your display to mirror the text. When the reflection is bounced off the teleprompter mirror, it appears back in the correct orientation. This allows you to use literally any PC program with your teleprompter rig.
DIY project using first surface mirror
Alternatively to using a first surface mirror, you can also buy an external video flipping box (HDMI MirrorBox)