Version 2.0 of LetsMonitor.org adds completely free HTTPS monitoring to its certificate expiration monitoring.
This is a major update,with the primary new feature being global HTTPS monitoring for functionality, availability and performance. Also, certificate monitors now have configurable expiration thresholds. Contacts are now more flexible and sets can be set up for escalations.
In addition, many fixes have been implemented, including confirmation tests to avoid false positives.
See it here: https://letsmonitor.org