Why is this question in the iPad Apps thread and not in the thread for Mac Apps?
In any case though here are a few of my essential apps:
BusyCal 2
OmniFocus 2
Day One
Evernote
YNAB 4
One Note
Office 365
Caffeine
And of course, the apple Apps that came with my iMac that I DO use everyday, Numbers, Pages, Keynote, iPhoto, Calendar, Mail, etc.