Are you looking for TCP or UDP multi-threaded servers?

Networking (local and internet) Synapse classes I use can be found here:

http://www.synapse.ararat.cz/doku.php/start

And some server examples here (see UDP server sample and TCP server links on that page):

http://www.synapse.ararat.cz/doku.php/public:howto

A bunch of different server/client demos also come with the source code when you download Synapse

cheers,
Paul