Checking App for Life
We usually just use a script that runs as a cron job. It hits a direct action on the app that returns a known "all is OK" response. If that does not get returned, alarms ring.
We use Nagios with the check_http plugin. This plugin actually make a HTTP (or HTTPS, if the plugin was compiled with openssl support) to our apps and check a DirectAction to see if it's answer "1". If not, Nagios send a trigger.