This tag corresponds to the version of MSBuild packaged with Visual Studio 2015 Update 3.
This release is also available via a standalone Build Tools 2015 Update 3 installer.
The only change to MSBuild since Update 3 RC was a fix for #705, which was an internal-only change not reflected in the GitHub source.
Important: the actual Update 3 release was not produced by compiling the GitHub source at this commit. It was built from a mirror of MSBuild in the Microsoft-internal VS repository, which was manually synced to contain the changes made here. These sources are instructive for behavior and understanding purposes, but not suitable for debugging the released binaries.