The W5100 TCP driver is intentionally very similiar to the UDP driver. It comes with its own test program (again similiar to the UDP test program) and an extension to the communication peer program to support the test program.
In order to ease exploring the W5100 UDP driver a simple test program using it was added. Additionally a communication peer program was introduced. The latter builds as-is for Windows using i.e. the VC++ command line 'cl w5100_peer.c'.
This file isn't technically related to ip65. It uses the W5100 IP stack to implement UDP frame RX/TX. The code heavily optimized for size (in contrast to speed).