The Sims:

A modders paradise.

The Sims, Will Wright's major hit in the early 2000's and one of the easiest games to create content for.
I spent a long time messing with the coding of objects, similar to the kind of Hacks C&C enterprises were about, an addition to vanilla, and by mostly self taught, and somewhat taught by C&C tutorials and much more advance IFF pencil and Advanced script editing trial and error, I created some rather extensively modded gameplay objects, including Makin' Magic charms and spells that are used like normal objects, a flamingo that maxs out motives and a bunch of chairs that spawn ingredients for your Sims. All my downloads are available in the Downloads section.