As a good project, L2.Net has documentation.

Documentation is based on Sandcastle Help File Builder ( thanks them a lot :) ).
Compiled CHM file can be found here: L2.Net.Documentation(19.05.08).chm.

If you want to make help files yourself, you can go to Sandcastle Help File Builder page for instructions, and then compile it using L2.Net.Documentation.shfb file in L2.Net.Scripting project root folder.