IBM's Microkernel, named Workplace OS microkernel, was the core components of Workplace OS, a portable successor of OS/2. The basic premise of Workplace OS work was: 1) IBM would adopt and improve the CMU Mach 3.0 microkernel for use on PDAs, the desktop, workstations, and massively parallel machines, and 2) that several operating system personalities would execute on the microkernel platform concurrently. This architecture would allow users to switch between applications written for different operating systems while IBM would also benefit by having one common platform for all product lines. The goals of the microkernel and the technical features of design are described in this paper. We also present lessons that may benefit future projects with similar goals."