LibLog 
Designed for specifically for library developers, LibLog is a single file for you to either copy/paste or install via nuget, into your library/framework/application to provide a logging abstraction. It also contains transparent built-in support for NLog, Log4Net, EntLib Logging, Serilog and Loupe, and allows your users to define a custom provider if necessary.
Please see Wiki for more informantion.
License
LibLog is licensed under MIT Licence.
Developed with:
Feedback, compliments or criticism: @randompunter