Simple Calendar - A simple calendar with events (optional recurring and reminders), week numbers and a customizable...
Google Calendar - Spend less time managing your day & more time enjoying it
Kontact - Kontact is the integrated Personal Information Manager of KDE.
Rainlendar - Rainlendar - Customizable desktop calendar
Calendar Lock PEA - Calendar Lock PEA is an encrypted desktop calendar with a day, week and month view. The shown calendars are never stored unencrypted on your disk, but exist only in the RAM. Platform-independent, Open Source, no installation or registration required.
Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.