Two pieces of software developed by two different groups of people. I don't believe there's any sharing of code between these projects.

WindowMaker tried to recreate the NeXTSTEP UI and succeeded admirably.

AfterStep might've started out trying to recreate the NeXTSTEP UI, but it went all kinds of crazy with colors and gradients. Since then its connection to NeXTSTEP has almost entirely been in name only.

AfterStep had millions of bells and whistles. And the default theme was too horrible and gaudy like an LSD trip.