Why Google wants to replace Gmail

Instead of tabs, Inbox groups together and labels and color-codes messages according to categories.

One key feature of Inbox is that it performs searches based on the content of your messages and augments your inbox with that additional information. One way to look at this is that, instead of grabbing extraneous relevant data based on the contents of your Gmail messages and slotting it into Google Now, it shows you those Google Now cards immediately, right there in your in-box.

Inbox identifies addresses, phone numbers and items (such as purchases and flights) that have additional information on the other side of a link, then makes those links live so you can take quick action on them.

You can also do mailbox-like "snoozing" to have messages go away and return at some future time.

You can also "pin" messages so they stick around, rather than being buried in the in-box avalanche.