In ROM Hacking, there are several types of utilities.
Game specific utilities are only useable in a specific game, and not for any other game. Lunar Magic is an example of a game-specific utility.
A Universal utility will work on all games. An example of a universal utility is YY-CHR, a tile editor that does not rely on any game, or even system-specific needs.
An Accessory utility is one that offers a nice bonus, but is not needed to make a hack. Block Tool is an accessory because you don't need custom blocks to make a hack.
Required Utilities are utilities that form the main and preferred interface for hacking ROMs. Lunar Magic is a Required Utility for SMW hacking.
NOTE: This assumes that Hex editors are not considered useable for hacking ROMS. We all know they actually are, though.