Guidde - A quick, context-based customer support widget
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
Juphy - Manage all your social media conversations, comments, reviews, and support requests in a single, shared inbox. Boost Sales on Social Channels via Messaging.
Helpwise - Shared inbox for your team email addresses
HelpScout - Help Scout is a simple, straightforward way to provide excellent support
Front - multi-channel inbox service for collaborative teams