InstaCal!

Keep track of your busy schedule and share it with others using Calendar. Create separate calendars — one for home, another for school, a third for work, and so on. See all your calendars in a single window or choose to see only the calendars you want. Calendar lets you create invitations using information from Contacts, update your guest list, keep track of responses, and receive the latest status information. When you or another Mac user receives a Calendar invitation via Mail, it’s automatically added. Calendar also works with iCloud, Yahoo!, and Google. And when you use iCloud, every Calendar edit you make on your Mac automatically appears on your iPad, iPhone, and iPod touch. So no dinner dates are missed, no meeting goes unattended, and no anniversary is forgotten. »

Rainlendar is a feature rich calendar application that is easy to use and doesn't take much space on your desktop. The application is platform independent so you can run it on all major operating systems: Windows, Linux and Mac OS X. The appearance can be customized with skins and you can even mix different skins together. It is possible to use Rainlendar with other calendar applications too. Rainlendar uses the standard iCalendar format to store its events and tasks so you can easily transfer them between applications. You can also subscribe to online calendars including the Google Calendar and edit your Outlook appointments directly in Rainlendar*. »

Fantastical is a flexible calendar with natural language event creation, a beautiful calendar and event list, support for CalDAV (including Google Calendar delegates) automatic alarms, and instant searching.

Kin Calendar is a simple yet connected calendar, developed as a Sunrise replacement.

Itsycal is a tiny calendar for your Mac menu bar. If you want, it will display your appointments and serve as a companion to the Mac Calendar app.

Take control of your schedule and get reminded wherever and however you want. Instantly access your appointments, tasks, and notes with a simple glance at a transparent calendar that sits right on your Windows desktop. Share calendars and reminders in your home, office, or online. Automatically synchronize with Google Calendar and Outlook. Print calendars using a wide variety of layouts and styles. You can do all these things and much more with VueMinder Calendar.

Day-O is a simple menu bar clock replacement with a simple calendar for your Mac. Which uses strftime style customisation.

Calendar 366 is the perfect menu bar mate for OS X's Calendar app. Click on the icon and get an overview of your events. Click on a date and see details, or switch to the expanded view* to see all upcoming events in just a single window.

Calendars 5 seamlessly syncs with local iOS calendars, Reminders and even Google Calendar.Now all your events and tasks are in a single application, which is always on hand.

qOrganizer is a general organizer that includes a calendar with schedule,reminders,journal/notes for every day, to-do list.But provides features useful for students such as:timetable and a booklet for marks and absences.It's designed to be easy to use.

Put a calendar on your menu bar, and access your calendar, weather, and more at a glance.

Peek is a simple to use calendar for your iPhone.