Engineering manager and architect for Microsoft’s “Industrial Metaverse” effort.Technical leader of a team responsible for building business solutions using the latest advances in reinforcement learning and machine teaching.Primary author of "pyright", Microsoft’s open-source Python static type checker.Previously led a team of developers in Redmond, Boston, Palo Alto and Prague responsible for building a new ground-up rewrite of the Skype consumer client across six different platforms.Before that, led a small team working on incubating group productivity solutions within the Office team and later the Skype team.

Cofounded startup company with Brent Traut. Worked on several product concepts including a photo management app and a group productivity service.

Led a team of about 200 engineers who were responsible for the Windows kernel, virtualization stack, file systems, storage, and security features of the operating system. Successfully delivered features for Windows 8 and Windows Server 2012, including support for ARM-based devices.

Led the team of engineers who were responsible for for continued development of the Windows kernel and virtualization stack. Successfully delivered features that appeared in Windows 7 and Windows Server 2008 R2.

Built and led a team of about 85 engineers and program managers responsible for the development of Microsoft's machine virtualization platform, eventually marketed under the name Hyper-V. This platform now provides the foundation for the Azure cloud, Windows Server, and Xbox.

Led the development of numerous software products, many of them based on emulation and virtualization technologies. Virtual PC allowed users to run PC operating systems (DOS, Windows, OS/2, Linux, etc.) and applications on a Mac. Later versions of Virtual PC — and a server version called Virtual Server — allowed PC users to run multiple instances of PC-based operating systems on a single machine. Virtual Game Station allowed users to run Playstation titles on their Macs or PCs. Microsoft acquired Connectix in 2003.

Worked as part of the MacOS team to add support for PowerPC hardware. Was responsible for development of a JIT (just-in-time) binary translator that converted 680x0 to PowerPC instructions.