Vimcal - Vimcal is the world’s fastest calendar, beautifully designed for people who work remotely and live in their calendars.
Plan - Plan is a better way to organize.
Kin Calendar - The simple and connected calendar
Calndr.link - Dead simple & free add to calendar links + API
Kin - Kin is money for the digital world. It is used to generate value through a shared, decentralized cryptocurrency in a digital ecosystem of apps and their users.
Add-to-Calendar Button Generator - This open source projects lets everybody create amazing buttons, where users can add events to their calendars.