Microsoft OS2 SDK 2.0 Pre-Release 2
Released 6/1/1990 by Microsoft and IBM
For IBM PC 386/486-based computers

The Microsoft OS/2 2.0 pre-release SDK contains many features that
differed from IBM's OS/2.

The same desktop GUI as OS/2 1.x, a flat 32-bit application
environment, unlike OS/2 1.x, the ability to use 16-bit drivers, DOS
compatibility implemented using a protected mode 386 virtual DOS
machine, and Microsoft LanManager networking.

Several resources with more information:

An actual look at Microsoft OS/2 2.0
https://virtuallyfun.com/2024/02/26/an-actual-look-at-microsoft-os-2-2-0/

The Future That Never Was
http://www.os2museum.com/wp/the-future-that-never-was/
