Flow-e is a visualization layer on top of your Gmail or Outlook inbox. It provides an elegant Kanban-like workflow that's combined with the ideas behind Inbox Zero and GTD. Flow-e eliminates the need of external task management tools and transforms your inbox into a central To Do app.
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
Sortd - Rated the #1 App for Gmail
Salesforce Service Cloud - Service Cloud integrates customer service with social networks and provides a self-service customer portal and knowledge base system.
Drag for Gmail - Transform Gmail into organized To Do lists (like Trello)
Zendesk Support - Social Customer Support and Help Desk and Ticketing
KanbanMail - A Kanban board for your emails.