Even now, the NeXTSTEP desktop is not dead. Of course, there are efforts like GNU Window Maker, which replicate the look and feel, and GNUstep, which duplicates the API. But what's not generally known is that the original desktop environment, if not quite the OS, still lives.
Most people have forgotten that in addition to NeXTSTEP and its immediate successor OPENSTEP for Mach, there were also OpenStep for Windows and OpenStep for Solaris. OpenStep for Windows, sometimes known as the Enterprise Object Framework, more or less died on the vine. It can still be persuaded to run under Windows 2000 and even Windows XP, but it is just as poor a fit there as it was on Windows NT, and has a few notable bogosities. OpenStep for Solaris, however, is a much better fit. It has been revamped and repackaged as LuBu OpenMagic, a desktop environment for modern versions of Solaris. Although it runs only on the SPARC platform, it is a modern and capable DE. It includes all of the standard NeXTSTEP tools, such as Mail.app, the Terminal, the text editor and Workspace Manager. It even includes Interface Builder. On top of all this, it uses much less RAM than JDS, and is easier on the eyes than CDE.
Have an old Sun workstation? Give it a shot!