Zendesk Inbox is described as 'free mobile-friendly email app for teams. Collaborate, add private notes, and follow key conversations. Get started instantly' and is an app in the Office & Productivity category. There are five alternatives to Zendesk Inbox for a variety of platforms, including Online / Web-based, SaaS, Mac, Windows and Linux. The best alternative is Front. It's not free, so if you're looking for a free alternative, you could try Hipporello or SharedBox. Other great apps like Zendesk Inbox are HEY (Paid) and Plumm (Paid).
Front is the first email management software for teams that integrates with the tools you already use. With Front, you can assign messages to teammates, write comments for internal collaboration or set reminders to respond later.
Single collaborative customer support dashboard for all of your projects. Chat with your customers and your team members using single workspace. If it's an email sent to firstname.lastname@example.org or a chat request from yourproject2.com, it all goes into the same Plumm inbox.