Those systems are still around, and people are still porting software to them. For instance Git which is a fairly popular package created in 2005 runs on at le

Those systems are still around, and people are still porting software to them. For instance Git which is a fairly popular package created in 2005 runs on at least: Linux, GNU, GNU/Hurd, GNU/Linux, Tru64 UNIX, GNU/kFreeBSD, SCO UnixWare, SCO UNIX SV, Darwin, various versions of Solaris, Cygwin, *BSD, AIX, IRIX, IRIX64, HP-UX, Windows, MINGW. Older packages like Perl and Emacs compile on a much wider range of systems.