Cron - Cron Calendar.
KosmoTime - The to do list with super powers
Vimcal - Vimcal is the world’s fastest calendar, beautifully designed for people who work remotely and live in their calendars.
Todo Tab - A privacy-first todo list
Gone - An ephemeral to-do list
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.