Deception Toolkit - Fred Cohen's set of scripts for building honeypots
DIPC - a toolkit for building distributed apps
Fake - Fake allows you to take over the IP address of another machine in the LAN by bringing up an additional interface and making use of ARP spoofing. The additional interface can be either a physical interface or an IP alias
FakeBO - fake a Back Orifice/Netbus Server to annoy the kiddiez
Hunt - session-hijacking, connection-killing, and more... highly recommended!
ISIC - IP stack integrity checker - tests the stability of an IP Stack and its component stacks (TCP, UDP, ICMP et. al.) It does this be generating random packets of the desired protocol. The packets can have tendancies. ie by default all packets have a 50% chance of having IP Options. The packets are then sent against the target machine to either penetrate its firewall rules or find bugs in the IP stack.
Neped - detect Linux promiscuous-mode NICs on your subnet
NIS+ - The goal is to implement a fully functional NIS+ support for Linux, which will work with GNU libc 2.x and maybe with Linux libc 5.x.
UCD-SNMP - UC-Davis SNMP implementation [http]