I'll admit I'm being a bit too broad with that comparison.
I'm referring to the some of the aspects of the UI more then the general look and feel.
Here's a fairly lengthy look at various graphical UIs...
http://www.catb.org/~esr/writings/taouu/taouu.htmlObviously with themes in the mix the comparison gets a little messy.
Specifically I'm referring to the up and down arrows below the sliders next to each other, the use in Workbench of groupings in the Workbench folder itself (IE the drives and folders which, if you look at NeXTStep interface in the link, is kind of what that menu on the left manages to do in grouping functions), the ability to call window functions from the upper left of a window (functions like close), the ability to maximize the window from the upper right, and if I recall the NeXTStep windows didn't have that narrow frame on the windows like Windows started using in 2.0 and above, much like Workbench used that bottom right corner facing arrow to free resize a window.
Obviously that doesn't make them the same.
However there are some things they share.
Sigmason