ArcaOS is an operating system based on OS/2, developed and marketed by Arca Noae, LLC under license from IBM. It was codenamed Blue Lion during its development. It builds on OS/2 Warp 4.52 by adding support for new hardware, fixing defects and limitations in the operating system, and by including new applications and tools, and includes some Linux/Unix tool compatibility. It is targeted at professional users who need to run their OS/2 applications on new hardware, as well as personal users of OS/2.

Like OS/2 Warp, ArcaOS is a 32-bit single user, multiprocessing, preemptive multitasking operating system for the x86 architecture. It is supported on both physical hardware and virtual machine hypervisors.

Source: Wikipedia (Accessed 2023-12-24): https://en.wikipedia.org/wiki/ArcaOS

The very last OS/2 released solely by IBM.

The beginning of the end with IBM’s primary role. Warp 4.0 was also more focused on the user market for personal computing in competition to Windows NT series.

Red spine included just the OS/2 Warp without Window 3.1 (although you can add it with a copy of Windows 3.1.) The Blue spine came with Windows 3.1.

The first client based user operating system to include SMP support.

The release of OS/2 2.1 came complete with a CD option for installing. You still needed either two 3.5″ or 5.25″ floppies to get the CD installer working.

The official release of OS/2 2.0

Limited availability, this was the first OS/2 release after Microsoft’s involvement with IBM.