Clearbit - Clearbit provides Business Intelligence APIs
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
ZoomInfo - ZoomInfo is a B2B database providing detailed business information on people and companies.
tawk.to - tawk.to is a free live chat app that lets you monitor and chat with visitors on your website or from a free customizable page
InsideView - InsideView aggregates and curates all the company and contact data, news and social insights, and professional connections you need to do business better.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.