Mobile Chat Kit - UI kits & sample apps for building in-app mobile chat
iOS Design Kit - The newest library of native iOS templates
Ambient Design - Ambient is a mobile app design market where you can get unique mobile UI kits.
Dashboard UI Kit - A modern & responsive dashboard UI kit for designers.
Bots UI Kit - Fully customizable Sketch UI Kit for Messenger Platform
Chat by Stream - Build and ship in app messaging in a few hours