Meetingbird for Gmail - View your calendar and schedule meetings right from Gmail
Lightning Calendar - Organize your life — it’s about time!
Mixmax Calendar - The fastest way to schedule meetings with anyone, anywhere
Simple Calendar - A simple calendar with events (optional recurring and reminders), week numbers and a customizable...
Kin Calendar - The simple and connected calendar
GMinder - GMinder is an open source Windows System Tray app that pops up to remind you about Google Calendar events.