InBoxer

Unofficial, free and open-source Google Inbox Desktop App

It's built on top of Inbox by Gmail web-version, has pleasant UI and supports useful keyboard shortcuts.

Features
Familiar Inbox by Gmail interface
Cross-platform (macOS/Linux/Windows)
Useful Keyboard shortcuts
Multiple accounts
Optional Always on Top
Auto-updates to the latest version
Desktop notifications
TODO: Dark theme
TODO: Custom text size
TODO: Ability to use as default mail client