Lidgren.Network is a networking library for .net framework which uses a single udp socket to deliver a simple API for connecting a client to a server, reading and sending messages. This is the third version of the library.

Basics tutorial

Incoming message types

Peer/Client discovery

Simulating bad network conditions

Unconnected messages

Sequence channels

Message encryption

Improvements over previous version

Download source and samples here; questions and feedback in the forum here.