Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
Userfeed - Product feedback made for Intercom
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Fider - Fider is an open source, cross platform and free to use customer feedback platform for companies...
Nylas Mail - The Nylas Cloud API powers your application with email, calendar & contacts features. Built-in features for better email, calendar, and contact management.
ClearFlask - Open-source Product Feedback Tool with a Public Roadmap and Announcements.