Midori: Microsoft’s Abandoned Post‑Windows Operating System Project

Midori was a secret Microsoft research project launched around 2008 with the ambition to create a next‑generation operating system that could eventually succeed Windows. The effort was led by senior executives such as Eric Rudder and featured Joe Duffy (later Pulumi CEO) as a key spokesperson.

The project gathered up to a hundred engineers and operated under a high level of secrecy. It was positioned as a cloud‑centric OS that would separate software from hardware, avoid the “spaghetti” architecture of traditional Windows, and remain compatible with existing Windows applications.

Technically, Midori was built around a microkernel written largely in native C++, with a new language called M# (an extension of C# and Sing#) introduced to improve performance and safety. Its design emphasized three pillars: cloud integration, massive concurrency, and strong security guarantees.

Team culture was distinctive: every member, including managers and architects, was required to write code and take ownership of testing and performance tuning. Duffy highlighted this as a major cultural advance within Microsoft’s R&D groups.

After seven years of development, Midori was cancelled in 2015. Microsoft cited a lack of clear commercial direction, and the project never reached a public release or open‑source stage. The experience left behind lessons about OS design, the challenges of replacing a dominant platform, and the importance of aligning technical ambition with business strategy.