Teamup Calendar - Cloud-based calendaring using capability URL, application developed in Zurich, Switzerland.

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

ApPHP Calendar - ApPHP Calendar is a PHP calendar script that may be easily integrated and used with various PHP projects, such as schedulers, event, etc.

Bringschuld - Simple periodic task and email monitoring

UpTo - Life goes beyond meetings and appointments

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