Itsycal is a tiny menu bar application for OS X that gives rapid access to a pop up view of the current month of the calendar.

Just click the menu bar icon (the current date by default) and a compact view of the current month is displayed. This is really handy  when you want to work out what day a particular date falls on for example. In addition you can configure it to show events from the next few days of your calendar rather than launching the Mac calendar app.

One of my favourite little time saver apps.