Source (required if based on other people's work): https://github.com/ImaginarySense/Teleprompter-Core
The most complete and professional free software teleprompter application.
Built with web technologies so anyone can customize it.
Features include: mirroring, dual-screen support, rich text editing, image support, custom styles, tablet mode, webcam mode, auto-save and accelerated graphics.
NOTE: This is only to provide appimages, I am not the developer.