Stim/Response Editor
From The DarkMod Wiki
This page needs to be completed, but I could find nothing else about the editor.
An example of setting up a response on an AI:
1) choose AI
2) Entity -> Stim/response editor
3) response tab
4) from the drop down menu choose Frob
5) right click response effects box on the right
6) add new effect
7) double click the newly added effect
8) effect: trigger (choose from drop down menu)
9) Target (name of your trigger_once)
Note: When using the stim/response editor, you must right-click on the Response Effects field in order to enter an effect (step 5). Not sure how anyone would know that.