tacmd is a command line tool used for ITM 6.x monitoring infrastructure management. There is a wide array of functions that you can use tacmd for. For example, you can use tacmd at the command line to edit agent configuration options, add a situation, create a situation, delete a situation, edit managed system lists, stop/start agents, and more. tacmd is a handy tool to have around.
The ITM Command Reference documents the capabilities of tacmd. Here's a link to the doc: