The FreeDOS operating system [1], started in 1994 by Jim Hall. Several critical parts of the system (e.g. the kernel) were written by others, but he is still coordinating the project in 2022. They released version 1.3 just recently.<p>Charles Childers' work on the tiny Retro Forth language [2] is also worth pointing out. It was started by Tom Novelli, but according to interwebs, Childers took over in 2001. Really cool language if you like tiny VM-based systems and forth.<p>Another tiny one-man language is PicoLisp [3]. Created by Alexander Burger in around 1988, and he's still the maintainer. He has been using it in commercial application development ever since.<p>Today, I'm wishing a long and healthy life to Virgil Dupras' Collapse OS! [4]<p>EDIT:<p>Another project I really like is Willus.com's k2pdfopt [5], a small cross-platform tool that optimizes pdf files for mobile readers. Started in around 2011; judging by the website, very probably a single-person thing.<p>One more is, edbrowse, a "command line editor browser" with ed-like command language [6]. Originally written in 2002 by Karl Dahlke for blind users, but might be interesting to many others as well because of its scripting abilites.<p>Ah, and also mhwaveedit [7], Magnus Hjorth's wave editor, developed by him since around 2002. And Mark Tyler's mtpaint [8], which was apparently very much inspired by mhwaveedit.<p>A fascinating single-person made digital audio workstation is Non DAW by Jonathan Moore Liles [9], started in around 2006. I've used it a lot, great modular design, ran really well on an old Thinkpad T42.<p>Serenity OS [10] has also been in development for 3 years. Andreas Kling's amazing effort.<p>Possibly Dwarf Fortress [11] would also almost count as a two-man project, by Tarn and Zach Adams, going on since 2002.<p>Nils M. Holm's creations also deserve a mention for sure. Scheme 9 From Empty Space, Klong array language, several books, etc [12]. Really inspiring guy.<p>Not wishing to turn HN into Wikipedia, so I'll stop here. The dedication behind this kind of projects is amazing, really.<p>1: <a href="https://www.freedos.org/" rel="nofollow">https://www.freedos.org/</a><p>2: <a href="http://retroforth.org/" rel="nofollow">http://retroforth.org/</a><p>3: <a href="https://picolisp.com/" rel="nofollow">https://picolisp.com/</a><p>4: <a href="http://collapseos.org/" rel="nofollow">http://collapseos.org/</a><p>5: <a href="https://www.willus.com/k2pdfopt/" rel="nofollow">https://www.willus.com/k2pdfopt/</a><p>6: <a href="http://edbrowse.org/" rel="nofollow">http://edbrowse.org/</a><p>7: <a href="https://github.com/magnush/mhwaveedit" rel="nofollow">https://github.com/magnush/mhwaveedit</a><p>8: <a href="https://en.wikipedia.org/wiki/MtPaint" rel="nofollow">https://en.wikipedia.org/wiki/MtPaint</a><p>9: <a href="http://non.tuxfamily.org/" rel="nofollow">http://non.tuxfamily.org/</a><p>10: <a href="http://serenityos.org/" rel="nofollow">http://serenityos.org/</a><p>11: <a href="https://en.wikipedia.org/wiki/Dwarf_Fortress" rel="nofollow">https://en.wikipedia.org/wiki/Dwarf_Fortress</a><p>12: <a href="http://t3x.org/s9fes/" rel="nofollow">http://t3x.org/s9fes/</a>