[dmarble]

Check out Legend (formerly moo.do): https://legendapp.com/

Found it several years ago and used it regularly for a while. It has a nice mixed model for blending calendar, email, lists, tasks. Lots of drag and drop capability, keyboard shortcuts. Loads fast. Mobile app. Customizable views you can quickly switch between, e.g. 3 column email on left, tasks in the middle, calendar on the right.