I'm going to miss Inbox. Sure they merged a bunch of features back into Gmail, but they still don't provide some of the greatest ones - such as context aware grouping. Planning a trip? All the emails from the various services you reserved (airfare, rental car, hotel, etc.) get grouped under "Your Trip to X" automatically. Or the grouping of GitHub emails under a group per repository or organization with buttons such as "view pull request" or "view issue."