At I/O 2015 Google announced that its smarter, task-based Inbox app is open to everyone and you won't need an invite to join in. There are some new features baked in as well. Inbox now categorizes all your Trip/Travel relates mails in one place, it also now shows you Google Keep reminders and suggests adding a reminder if someone sends you a to-do list.
"Undo Send" has also been added, although that has been available standard GMail for quite some time. You can add custom signatures, open reservations in connected apps like Eat24 and HotelTonight
Source: Official GMail Blog
