Meetingbird for Gmail - View your calendar and schedule meetings right from Gmail
Vimcal - Vimcal is the world’s fastest calendar, beautifully designed for people who work remotely and live in their calendars.
Kin Calendar - The simple and connected calendar
Clean Google Calendar - Makes Google Calendar look nicer & launches as a desktop app
Calendly for Chrome - Schedule meetings without leaving your inbox
Plan - Plan is a better way to organize.