Day-O is a utility that comes as an alternative to using Mac's default clock tool to check the time and date from your status bar. This program not only displays the current time, but it also gives you access to an integrated calendar tool, a feature that's obviously missing from the Mac default application.
Keeping two clock tools in your status bar is pointless and space-consuming. You can hide the default clock tool from your Menu Bar by going to System Preferences panel and disabling the "Show date and time in the menu bar" option from the Clock window.
The application's icon is placed on your status bar and next to it you can see the current time. By clicking over the icon you reveal the app's main menu and the built-in calendar tool. The program features options to set the time format (hour minutes PM/AM), start the app at system login, and hide or reveal the tool's icon in the status bar.
Day-O doesn't give you access to many features and settings. For instance, you cannot change the appearance of the calendar, add notes or events to certain dates, etc. The simple calendar tool is the only difference between this app and Mac's default clock tool.
Even though the utility comes without a price tag, I still don't think it's worth installing it on your Mac. Personally, I prefer using Mac's default clock and calendar apps as they offer me more useful features.