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.
Sortd - Rated the #1 App for Gmail
Drift - A messaging app that helps you grow your business.
Drag for Gmail - Transform Gmail into organized To Do lists (like Trello)
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
KanbanMail - A Kanban board for your emails.
Tars - TARS enables users to create chatbots that replaces regular old webforms.