Mini Calendar is a lightweight menu bar app, which helps you to access your monthly calendar. It can display just an icon with the date, but also the time, the day of the week and the sunrise and sundown times.
Quickly see your next meeting right in your menu bar.
Overdo is a menu bar app that lets you quickly and easily schedule deadlines.
TinyCal gives you easy access to Google Calendar or Apple Calendar, straight from the menubar. Add events, reminders, lots of options. TinyCal can show multiple months, use custom calendars, show holidays from many countries and multiple personal/business calendars.