I bet you could compile an old Xlib (or Xt/Motif) application on Linux, but good luck running a binary from way back when -- the libc/glibc and a.out/ELF switch

I bet you could compile an old Xlib (or Xt/Motif) application on Linux, but good luck running a binary from way back when -- the libc/glibc and a.out/ELF switch should put breaks on that. On the other hand, if your actual premise is open source, there's simply less incentive of avoiding breaking binary compatibility. I bet there were a few angry words and stomped feet in the last decades at Microsoft because of having to maintain that. Not that glib/gtk are poster childs for even source-level compatibility, not even within one major version. There's a reason why several projects are switching to Qt. (I'm doing my Cato bit here: I still think that they should've done an Xt toolkit instead of inventing the wheel yet again. There certainly was some experience there, given that GIMP 0.x was written for Motif.)