NLog

NLog is a .NET logging library designed with simplicity and flexibility in mind. With NLog you can process diagnostic messages emitted from any .NET language, augment them with contextual information, format them according to your preference and send them to one or more targets.

The API (application programming interface) is similar to log4net, and the configuration is very simple. NLog uses a routing table while log4net uses a logger hierarchy with attachable appenders. This makes NLog's configuration very easy to read and maintain.

NLog is licensed under the terms of BSD license, which permits commercial use and the source code is available to anyone at no cost. Everyone is encouraged to test it and report feedback to the mailing list.

NLog supports .NET, C/C++ and COM interop API so that all your application components including legacy modules written in C++/COM can send their messages through a common log routing engine.

The .NET API is very fast at filtering messages, so that you can keep your logging instructions in code and let NLog filter them out at runtime. NLog can filter out as many as 150 million logging instructions per second on a single-CPU 1.6 GHz laptop. Add that to asynchronous processing and other wrappers and you'll get a very powerful and scalable logging tool.

Look for more information
http://www.nlog-project.org/