There's also ProseMirror [1], which I'm told is very good, and supports extensions of its document model to support things like embedded objects and Markdown, a

There's also ProseMirror [1], which I'm told is very good, and supports extensions of its document model to support things like embedded objects and Markdown, and is designed for collaborative editing -- all document operations are patches that can be sent over the network. [1] http://prosemirror.net/ http://prosemirror.net/