You can also create plugins with C# language, compile that into a DLL and put into Sifon folder. That would work in the same manner as PowerShell plugins.
Of course, unlike PowerShell such plugins do not support remote profiles out of the box and author may need undertaking additional effort for adding such a support, or just leave them working as local-only.
There's a separate demo project with such plugins examples, that get compiled into a DLL. You may find it here:
https://github.com/MartinMiles/Sifon.Plugins.Example.git
Please note: there is a dependency to Sifon.Abstractions library