Cron - Cron Calendar.
Gone - An ephemeral to-do list
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.
Streaks - The to-do list that helps you form good habits.
zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.