Leading libraries for .NET didn't allow for all of the possible options (including honeypot and test fields). This library is fully featured including:
The other libraries were typically .NET Standard only or .NET Core 3+ only. As we had full framework projects that would benefit from Akismet these weren't options (due to issues decribed here: https://github.com/dotnet/standard/issues/542, which may or may not be fixed). I needed a library that also targeted the full .NET Framework to resolve these issues. I also wanted to be able to use the other features that were missing from the other libraries.
Check out the full project here: https://github.com/ahwm/Akismet.Net
Building this library allowed me to also create a plugin for Umbraco: https://github.com/ahwm/Akismet.Umbraco.
The Umbraco plugin allows a site administrator to review comments/submissions and report spam/false positive as well as set the configuration.