log4net is a tool to help the programmer output log statements to a variety of output targets. log4net is a port of the log4j framework to the .NET runtime. They have kept the framework as similar to the original log4j as much as possible,
log4net is part of the Apache Logging Services project. The Logging Services project is intended to provide cross-language logging services for purposes of application debugging and auditing.
Check it out here.