Hotline - In-app chat,real-time engagement & self-service for your app
Semrush App Center - Power your marketing by connecting your apps to Semrush data
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Outbound Apps by Intercom - Embed apps right inside your messages
Nudgespot - Nudge your customer (via email etc) to take the next step
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.