Fear

Fear is a mapmaking app from Bungie used for creating new units, physics, sounds, scenery, etc. It was bundled with Myth II: Soulblighter

In Myth-speak, Fear is a tag editor. A tag is a small small data structure that Myth uses to store all sorts of information, from models to sounds to unit definitions. Simply think of them as data files for Myth, and you should have no problems.

As of early 2014, the latest version of Fear (& Myth) is v1.8. An updater can be found here, and the related Fear 1.8 documentation here.