Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.

Digsby - Tagged makes it easy to meet and socialize with new people through games, shared interests, friend suggestions, browsing profiles, and much more.

Service - Customer service issues solved for you, on demand, for free.

WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.

LiveMessage from Salesforce - Make mobile messaging a cornerstone of customer service

Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.