ZenDesk - Zendesk is a beautiful, lightweight help-desk solution.
Salesforce - CRM software solutions and enterprise cloud computing from salesforce.com, the leader in CRM and platform as a service.
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
Mautic - Mautic is marketing automation software (email, social, & more).
HelpScout - Help Scout is a simple, straightforward way to provide excellent support
Insightly - Insightly is the easy, powerful and affordable online Customer Relationship & Project Management Software used by over 400,000 small businesses world wide