SendBird - SendBird is messaging-as-a-service.
Mobile Chat Kit - UI kits & sample apps for building in-app mobile chat
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Kait.ai - Connecting People With Brands
Chat by Stream - Build and ship in app messaging in a few hours
Ambient Design - Ambient is a mobile app design market where you can get unique mobile UI kits.