Mac: For whatever reason, Apple's Calendar app doesn't include a menubar app. Itsycal is a tiny little app that adds that exact function and hooks it right into Calendar.
Itsycal is very simple, but it's also very handy. You can have it display just a calendar for the month or hop into the app's settings to also also show your events. You can then easily open up Calendar directly from Itsycal. It's not as powerful as a menubar calendar app like Fantastical, but it's free and hooks right into Calendar.