LibLog 
Designed specifically for library developers, LibLog is a source code package that you install via nuget into your library/framework/application to provide a logging abstraction. It also contains transparent built-in support for NLog, Log4Net, Serilog and Loupe, and allows your users to define a custom provider if necessary.
Please see Wiki for more information.
Availability for old csproj format
LibLog uses .pp file to do a namespace transform (aka source
transform)
so it fits into your project's namespace. This is handled transparently by the
new dotnet sdk as of LibLog version 5.0.0. If you change your project's root
namespace then LibLog will automatically change also. For older project
formats, please continue to use LibLog 4.x versions.
License
LibLog is licensed under MIT Licence.
Feedback, compliments or criticism: @randompunter