From the article, the time to beat is November 16, 1992. This might be possible on one of the BSDs, as FreeBSD and NetBSD both document support for running a.out executables with the 4.3BSD ABI. I guess it would depend on whether anyone had ported X11 to run on a BSD on i386 before then. Alternatively, maybe you'd be able to get something running on SCO OpenServer (if you count that as a current OS, it IS still getting security patches). It documents support for XENIX x.out binaries ( https://www.scosales.com/ta/kb/126704.html ) so you might be able to run software compiled in the late 1980s for XENIX/386.