Are you a game designer, either an amateur or professional?  Have you ever found it difficult to go from a design document to concrete gameplay?  Do things that looked good in the design doc give you trouble when it comes to implementing it?  Wouldn’t it be nice if your design document was your implementation and you could drop your gameplay right into the engine by copying files and restarting?  If you are working on a new engine for the first time, wouldn’t it be nice if you could reach into your previous work and

Are you a modder?  Have you ever found yourself spending more time and energy fighting the platform that you are trying to mod than building your dream?  Most moddable virtual world platforms, be they old school MUD codebases such as Diku, or more modern platforms such as Neverwinter Nights or Minions of Mirth are built from the ground up to be one game.  Turning them into “your” creature is akin to remodeling a house.  It can be done; people do it all the time.  But wouldn’t it be nice if you had an easy way to exchange the platform’s default ruleset with your one.