Top alternatives for Redactor
I have a startup (Bybrand), which the core of the product is the Froala Editor. The editor is updated frequently.
AxMath is an interactive WYSIWYG equation editor. It enables you to type formulas faster than handwriting. It has all kinds of functionalities which make you type equations at lightspeed. Key features include semantic math input, auto calculation, LaTeX conversion, memory board, etc. It currently supports Win7/8/10 and Office 2010-2016.