Mailbox. The cross platform email client bought and abandoned by Dropbox. To date, I have not found a cross platform (or really any single platform) app that's

Mailbox. The cross platform email client bought and abandoned by Dropbox. To date, I have not found a cross platform (or really any single platform) app that's as fast as Mailbox. I don't know how they did it, but everything felt truly instant. All of my devices would simultaneously ring when an email arrived. Archiving/deleting/snoozing emails instantly synced across all platforms (including the web Gmail client). The aesthetics of Mailbox remains unmatched by any email client available today.