Log4Net is a simple and effective logging solution for .Net applications. If you want to use it with the .NET Compact Framework, you just need to recompile the source code that is part of the standard 1.2.10 (zip) download package. Open the solution file (.sln), make sure build is set to Release, and compile with symbols NETCF and NETCF_1_0 defined in the log4net project properties [don’t forget to update the assembly references to point to the Compact Framework 2.0 SP2 DLLs, rather than the standard framework ones]
(Note: although we are compiling for CF 2.0 there is no NETCF_2_0 symbol to define)
What are the differences between the Compact and Standard versions? http://logging.apache.org/log4net/release/framework-support.html