Service - Customer service issues solved for you, on demand, for free.
HelpStack - Open Source mobile help framework to support iOS and Android app users.
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Chat Center - Chat with one click, no matter what messaging app you use
LiveMessage from Salesforce - Make mobile messaging a cornerstone of customer service
Helpshift - Helpshift is an in-game customer support platform that enables mobile apps to improve customer experience, drive higher ratings and increase retention.