Cron - Cron Calendar.
Nirow - Habit tracking: Automated, Siri-ed, Calendar-ed, and More!
zcal - zcal is the fastest way to schedule every meeting for Free and make it personal.
Streaky - Achieve daily goals and build your personal streak 🔥
Cal.com - Cal.com (formerly Calendso) is the open source Calendly alternative.
Taskful - Deadlines, meet your match.