The Microsoft Build Engine is a platform for building applications. This engine, which is also known as MSBuild, provides an XML schema for a project file that controls how the build platform processes and builds software. Visual Studio uses MSBuild, but it doesn’t depend on Visual Studio. By invoking msbuild.exe on your project or solution file, you can orchestrate and build products in environments where Visual Studio isn’t installed.
Visual Studio uses MSBuild to load and build managed projects. The project files in Visual Studio (.csproj,.vbproj, vcxproj, and others) contain MSBuild XML code that executes when you build a project by using the IDE. Visual Studio projects import all the necessary settings and build processes to do typical development work, but you can extend or modify them from within Visual Studio or by using an XML editor.
Microsoft has now open sourced MSBuild and the source code is now available on Github. Find it here.