ProseMirror is a toolkit for building rich-text editors on the web.
Powerful, low-level API; Not tied to a context (React, etc); Very flexible and modular; Rock solid output;
Bit of a steep learning curve, docs could be better
We've used ProseMirror for our components at simpla.io since it was in alpha, because it was the only framework that was low-level and flexible enough to achieve what we wanted (semantic output, inline editing, custom doc model). Since then it's only gotten more powerful and stable. In my opinion it is the best richtext editing framework currently available, without exception.Sean King has used this product for one year.