In the "Hilscher EtherNet/IP Tool," a software scanner, you'll find the LibEtherNetIPV2.dll alongside the corresponding .pdb file. This library provides basic functionality for both the adapter and scanner sides, primarily handling lower level stuff like message parsing, data production/consumption, and timeout management.

While the library itself is not formally documented, it's offered as a debug build and is available for free. However, creating a fully functional adapter will require you to implement a lot more, such as TCP and UDP server bits, the full object dictionary, message dispatching, and a ton of other features.

This tool is my baby, and we also have a C#-based Software Adapter that uses the library. It's just a skeleton we use as a dummy peer for testing our own scanner products. It is not distributed.

So, since there was no other response, for experiments, and if the topic is still of interest, you may want to take a look at the lib with a reflection tool, like dotPeek, which should allow you to peek into somthing which is close to the original source code.