Software Name: msbuild
Product Homepage: http://www.mono-project.com
Why should this be included in the repository?
Latest monodevelop stable release makes use of msbuild, which is a rewrite of Microsoft's msbuild. Previous versions of monodevelop made use of xbuild instead, which wasn't feature-complete compared to the Microsoft's command. Starting from mono 5.0.0, mono's msbuild is 100% complete and MonoDevelop switched to it, but it's in a separate repository. Info here
Open Source: Yes
How many users do you anticipate will use this software? I don't know, but it's required ?
Source tarball: https://github.com/mono/msbuild/archive/d15.2.tar.gz
Please note that latest release is pretty old compared to the master branch.