Google Calendar - Spend less time managing your day & more time enjoying it
Sortd - Rated the #1 App for Gmail
Mixmax Calendar - The fastest way to schedule meetings with anyone, anywhere
KanbanMail - A Kanban board for your emails.
Sunsama - Calendar and scheduling for teams
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.