mcron - mcron is GNU's implementation of cron. It is a 100% compatible replacement for Vixie cron.

Trello Calendar Connector by Cronofy - See and Organize your Trello deadlines inside your calendar

Anacron - Anacron is a periodic command scheduler. It executes commands at intervals specified in days.

Bringschuld - Simple periodic task and email monitoring

fcron - Fcron is a scheduler designed for Unix/Linux systems, especially usefull when your system is not up all the day long.

Cronitor - Monitor cron jobs, micro-services, daemons and almost anything else, no setup required. Easier cron troubleshooting and no more silent failures.