Windows Longhorn build 3683 is a Milestone 3 build of Windows Longhorn and is currently the earliest leaked build of Longhorn. The build was leaked in November 2002 by XBetas, and their effect can be seen in the setup handle (advertising for their now long-gone IRC channel). This build is most notable for being the first build to introduce the Plex theme and Windows Sidebar, alongside many features that would be used in later Longhorn builds such as Desktop Composition Engine and Windows Future Storage (WinFS).
This build still uses the i386 installation used in previous versions of Windows (and as such still has the same minimum requirements as Windows XP). However, using
winnt.exe to install has been unsupported and no longer works.