I downloaded the 2.8 zipped source code, unzipped it opened the CSharpDriver.sln in Visual Studio 2015.
The solution loaded but all projects failed to load with the following error:
"The default XML namespace of the project must be the MSBuild XML namespace. If the project is authored in the MSBuild 2003 format, please add xmlns="http://schemas.microsoft.com/developer/msbuild/2003" to the <Project> element. If the project has been authored in the old 1.0 or 1.2 format, please convert it to MSBuild 2003 format."