Knock has been great! We use Knock to serve feed-based content across channels, as well as handle our APNS notification needs.
ProseMirror has helped us quickly deploy a number of document-like scenarios, likes customer notes and lyric writing within our web apps and internal publishing tools.
We've been using Redwood to rapidly prototype, refine and ship a web-based solution to our customers that enables rich media sharing, collaboration. social interactions.