David L. Clark wrote Sopwith in 1984 as a trade-show demo for a networking product, not a commercial release. He had no idea it had gotten loose until around 2000 — by then it had spent over a decade circulating through IBM PC game collections, showing up unattributed in PC Magazine compilations within a couple of years of its creation. Simon Howard’s SDL Sopwith runs the original DOS source, changelog comments from 1984 intact, free in a browser.