OS/2—which was, at one time, IBM's competitor to Windows—continues to enjoy an extended afterlife, following the end of principal development in 1996. In 2015, Arca Noae announced a new, licensed distribution of OS/2—bundling new software and device drivers written for OS/2 with a new installer—with initial release in 2017 as ArcaOS 5.0 "Blue Lion."
Maintaining a decades-old operating system presents a variety of development problems far outside the mainstream, with solutions for those problems requiring a great deal of creativity to not break compatibility with existing drivers or programs. One of the most pressing issues facing OS/2 is the impending removal of the legacy BIOS Compatibility Support Module (CSM) starting in January 2020.
Compared to DOS, which extensively utilizes BIOS functionality, OS/2 has hard dependencies on only a subset of BIOS features, according to Arca Noae developer Alex Taylor, in a presentation at Warpstock Europe, posted to YouTube this week. The BIOS-supplied INT10 and INT13—VGA hardware and disk I/O via BIOS, respectively—are needed to boot ArcaOS