Vimcal - Vimcal is the world’s fastest calendar, beautifully designed for people who work remotely and live in their calendars.
Clean Google Calendar - Makes Google Calendar look nicer & launches as a desktop app
Calendarist - Time blocking companion for Google Calendar
Plan - Plan is a better way to organize.
Amie - GitHub for research and data science
Calndr.link - Dead simple & free add to calendar links + API