WysiHat is an incredible editor. Light, extensible, clean code, just great stuff.
The maintenance of Wysihat at Altruja has accumulated into something that works better than anything else in 2014 if you essentially just want a contenteditable that works without a lot of overhead, and where you can hack and control everything without a lot of fuss. You know. When you need an interface that works great on touchscreens, tomorrow. Or have a pesky UX vision that won't go away. Or something.
But it's not wysihat any more. It still looks and acts that way, but it's different. But I still can't believe it's not wysihat.
Get a textarea and call:
$('#myTextArea').whyzz();
Miracle Whyzz is released under the MIT license.