CKEditor - Real-time collaborative future-ready rich text editor
JavaScript - Lightweight, interpreted, object-oriented language with first-class functions
Summernote - Summernote is a JavaScript library that helps users create WYSIWYG editors online.
Allegro - Allegro 4 and Allegro 5 are cross-platform, libraries mainly aimed at video game and multimedia...
Froala Editor - Froala Editor is a WYSIWYG HTML editor that enables rich text editing capabilities for the applications.
Qt - Powerful, flexible and easy to use, Qt will help you not only meet your tight deadline, but also reduce the maintainable code by an astonishing percentage.