[i_have_to_speak]

Here's a command-line one written in Go: https://www.opsdash.com/blog/check-ssl-certificate.html

[stevekemp]

If you clone my sysadmin utilities, from here:

https://github.com/skx/sysadmin-util

You'll find:

     $ ssl-expiry-date bbc.co.uk
     bbc.co.uk
        Expires: Mar 15 17:01:06 2017 GMT
        Days: 289

That uses openssl, bash, and other standard facilities available upon Unix/Linux systems.