Unofficial, free and open-source Google Inbox Desktop App. Built using electron, Inboxer includes a menu bar which is globalmenu compatible and works, and keyboard shortcuts.
OpenMailBox Alternatives
OpenMailBox is described as 'Our online solution offers free e-mail address hosting for a wide public in search of a high quality service inspired by a free philosophy and totally independent of all the existing large service companies on the web' and is a popular webmail provider in the office & productivity category. There are more than 25 alternatives to OpenMailBox, not only websites but also apps for a variety of platforms, including Android, iPhone, iPad and Android Tablet apps. The best OpenMailBox alternative is Proton Mail, which is both free and Open Source. Other great sites and apps similar to OpenMailBox are Gmail, Tuta Mail, mailbox and Outlook.com.