Apple Calendar!

Microsoft Outlook, part of the Microsoft Office Suite (not to be confused with Microsoft Outlook Express), is a personal information manager that lets you manage your e-mail, calendar, contacts, and tasks.

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.

Why?

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

An offline calendar without any other calendar integration. You can easily create recurring events and setup reminders, it can also display week numbers.

Android calendar-app showing the weeks of the year (week numbers), 21 languages, syncable with Google Calendar: FEATURES* intuitive navigation with smooth transitions* day, week & month calendar* 48 colors per calendar, per-event color if supported by the calendar (Android Jelly Bean with Google Calendar only)* flexible recurrences (e.g., every 3 weeks)* birthdays & anniversaries with photos from your addressbook and editing* Fullscreen widgets* custom event font size* uses Android's native calendar backend and synchronization* no battery drain* moon phases and zodiac signs for birthdays* QR barcode sharing of events* NFC sharing (if supported by the device) NEW* free* no adsTRANSLATIONSnative language support for English, Arabic, Czech, Danish, Dutch, German, Greek, Spanish, Finnish, French, Hebrew, Italian, Japanese, Korean, Polish, Portuguese, Russian, Slovak, Swedish, Turkish and Chinese with more to come »

California is a new calendar application for GNOME 3. It's currently under heavy development.

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.

Dials' unique clock-based view of your day is easier and faster to view than the standard “list view” format other mobile calendars use. Dials' “one hand, one thumb” entry and edit of events also makes Dials the easiest and best on-the-go way to manage your schedule.

CalenGoo gives you a fast and easy way to access and change your Google Calendar (or Google Apps Calendar) with your Android device. It can either work with the built-in calendar or it can sync directly with Google.

BEAUTIFULLY DESIGNEDDigiCal’s diary planner and organizer provides a clear and beautiful overview for your events and appointments.• Conveniently switch between 7 calendar views (day, week, week agenda, month calendar, text month, year and list view in portrait and landscape mode).• The slick dark theme allows for better visibility in low-light settings and night mode.• Event keyword image matching available in all 27 languages!• 6 highly customizable widgets with different theme styles and views: (FREE: list, day, day list, day grid widgets; PREMIUM: 2 extra widgets –text month and month calendar widget)• Intuitive navigation between days, weeks and months with zoomable day and week view. »