Fast Forward accepts TCP or UDP connections on one address and port, and forward them off to some other address and port.
Firepass is a tunneling tool, allowing to bypass firewall restrictions and encapsulate data flows inside legal ones to use HTTP POST requests. TCP or UDP based protocols may be tunneled with Firepass.
nat-traverse establishes connections between nodes which are behind NAT gateways, i.e. hosts which do not have public IP addresses. Additionally, you can setup a small VPN by using pppd on top of nat-traverse. nat-traverse does not need an external server on the Internet, and it isn't necessary to reconfigure the involved NAT gateways, either. nat-traverse works out-of-the-box.
Netcast is a tool for single-source, multiple-destination, synchronous data transmission using multicasting udp stream for data and tcp connections for synchronization & control data.
Serveez is a server framework. It provides routines and help for implementing IP based servers (currently TCP and UDP).
SquTUN (pronounced "skew-ton") creates an AES-encrypted, SHA-1 authenticated UDP tunnel over which IP packets received from a TUN interface are encapsulated and transmitted.
UDP Cast is a file transfer tool that can send data simultaneously to many destinations on a LAN.
UDP File Transporter
UDP File Transporter consists of two command-line programs: a server and a client. Clients connect to a server in order to download and upload files using a protocol built on the UDP.
UDP Samplicator receives UDP datagrams on a given port, and resends those datagrams to a specified set of receivers.
udpfwd is a stateful userspace UDP port forwarder that can accomplish SNAT/DNAT. It listens for packets received on a given port, changes their source IP addresses to the address of the local host ("SNAT"), and forwards them to the destination (dest_ip:dest_port) from a randomly chosen local sending port. Once chosen, the source_ip:source_port:send_port triplet is unique, allowing for connection tracking. Conversely, when a packet is received on send_port, its destination is changed to source_ip:source_port ("DNAT"), and forwarded onwards.
uinetd is a very simple and small UDP packet forwarder. It is ideal for NAT networks.