Vimcal - Vimcal is the world’s fastest calendar, beautifully designed for people who work remotely and live in their calendars.
Amie - GitHub for research and data science
Button for Google Calendar™ - See your daily schedule and join meetings in one-click.
Cron - Cron Calendar.
Calendarist - Time blocking companion for Google Calendar
Nook Calendar - Know your team's whereabouts and availability. Get live updates on your team's current focus. Coordinate when and how you want to work.