UDPClient_Server is a project mainly written in Java, it's free.
A UDP server featuring reliable data transfer
Author: Joshua Kovach
A UDP Server/Client pair featuring reliable data transfer.
The Client will request a file from the /home/user/server directory. When downloading, the user can specify a packet success rate. If a packet is rejected, the client doesn't send an acknowledgement, and the server will resend after a given timeout. Files are downloaded to the /home/user/client directory.