refers to the interfaces to the black box with which software developers typically interact, then it is largely true that Windows is based on .NET because .NET

refers to the interfaces to the black box with which software developers typically interact, then it is largely true that Windows is based on .NET because .NET provides control of the operating system for the vast majority of projects I agree that the vast majority of Windows thick client business projects developed in the last few years probably target .NET, but, looking at the start menu on my Vista laptop currently, apart from dev tools, PAINT.NET and Keepass 2.0 (which still maintains a 1.x Win32 release), every other end-user application installed on my machine does not run on .NET. EDIT: In fact, I only run Keepass 2.0 for Mono compatibility on Ubuntu. I also would guess that a default Ubuntu desktop install has more dependencies on Mono, than a default Windows install does on .NET.