You can design and sell objects. The objects can consist of a 3d model and some programming to give it functionality. Example include clothing and body modifications; furniture and buildings; vehicles like planes, boats and dragons; and all sorts of other stuff.

There's a lot of possibility in SL, it's a shame that interacting with it is so clunky and awkward.

There's a lot to be said for it, but it is clunky, and hard to learn ...

OTOH there's WOW, which is better looking and easier to get started in. They're heading for 12-million users, which at $15/month makes SL look like Woolworth's.

But the ability to design objects, do shows et al means that for Maker-types the equal of SL exists nowhere else (that I know of).