Grit Game Engine - The Grit Game Engine is an MIT-Licensed Open Source Game Engine that is highly scriptable via Lua.
CKEditor - Real-time collaborative future-ready rich text editor
libtwo - All-purpose c++ app prototyping library, focused towards live graphical apps and games
Summernote - Summernote is a JavaScript library that helps users create WYSIWYG editors online.
MOS - Lightweight game engine.
Froala Editor - Froala Editor is a WYSIWYG HTML editor that enables rich text editing capabilities for the applications.