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.
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.
GMinder - GMinder is an open source Windows System Tray app that pops up to remind you about Google Calendar events.
WhenWorks - Mobile appointment scheduling
Simple Calendar - A simple calendar with events (optional recurring and reminders), week numbers and a customizable...
Inspora - virtual chat-stylist for fashion advice.