[arnehormann]

And how about Codemirror? It's mainly used for monospace code editing and it's missing a UI and editing widgets, but the configurability and maturity should blow everything else out of the water. A demo showing it's not only usable for monospace fonts in a single font-size: http://codemirror.net/demo/variableheight.html

[nomadcoop]

I really like Codemirror, it was simple to get set up in https://storytel.la/ and easy to extend. I'm a few versions behind and didn't realise it handles mixed width fonts, so thanks for mentioning it.