From CT3

The Embedded Event Manager (EEM) is a subsystem in Cisco IOS that can react to a number of events occurring in the router, from syslog messages and operator commands to changes in SNMP variables or Embedded Resource Manager policies. You can also define your own events or trigger timer-based or cron [1]-based events.

EEM-detected events are processed by EEM applets (extremely simple language entered directly into router's configuration) or EEM policies (Tcl scripts).

To get Cisco's EEM documentation, search their web site for EEM or Embedded Event Manager; I will not include direct links to their documentation as they tend to change the URLs and break the old ones recently.

If you want to add your own EEM applet to CT³, open the EEM applet page and follow the instructions in the right sidebar. To add a Tcl EEM policy, please go to the Tcl page.