I’ve bumped into this a few times when downloading other people’s code, but I hadn’t actually spent any time using it. Basically, log4net is a .NET implementation of the popular log4j logging system for Java.
I have to say, I like it a lot. You embed logging logic into your code specifying the message level (e.g. DEBUG, ERROR, etc.). Then at run time, not compile time, you configure how these messages get logged and where they should be logged. You can log to the Event Log, files, ADO databases, SMTP… even Windows Messenger (not IM, though).
It is very extensible, so you can add all kinds of new ways to log events. This is a must have for anyone writing web services, windows services, or any other code where you need good logging.