ADCH++ is a reference hub (server) implementation for the ADC (Advanced Direct Connect) network. It supports Windows / Unix platforms and is extensible with scripts in lua and python (so far) as well as C++ plugins.
NextHub is a powerful file-sharing server written in C#. It implements the ADC protocol and will run under any platform supporting the .NET 2.0 framework. The emphasis on NextHub is performance, simplicity, and extendability.