SendBird - SendBird is messaging-as-a-service.
Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Platforma - Wireframe library of layouts and UI elements
Live800 - Live800 is an enterprise-grade Live Chat and Customer Service platform that enables businesses to provide instant support to their customers through a variety of channels, including Live Chat, Email, Phone, and Social Media.
iOS Wireframing UX Kit - An easy, speedy way to wireframe for iOS