Check_certificate is a project mainly written in ..., it's free.
Nagios monitoring plugin to monitor a certificate and warn before expiration
check_certificate
This Nagios monitor makes it possible to check for pending certificate expirations and receive warnings and critical notifications as appropriate. It can be used for any TCP service that uses SSL (including https and ldaps).
The most complete and up to date information about this script can be found at:
To install this Nagios monitor, just copy the "check_certificate" file to your Nagios scripts directory.