[huntaub]

Mailbox is an all-in-one email client. Gmail is a webmail client for your (singular) Gmail account.

[toomuchtodo]

Gmail on mobile (both Android and iOS) both handle multiple Gmail accounts gracefully (personal, google apps, etc). To merge them seamlessly in the interface would be trivial.

[kristofferR]

In this case I was talking about Inbox, which in my mind should be a all-in-one gmail inbox.