Basic Broadcaster (bb) allows you to transfer text messages simply from one computer to another on a LAN. The messages are broadcast in the LAN and and can be received by each machine running bb. No setup is required other than starting the application. The messages are transmitted as plain text, and no encryption is done. The broadcasts can only be sent to machines on the same subnet as the sending machine, and will not be forwarded by routers to the Internet.
pidgin privacy please is a pidgin plugin to stop spammers from annoying you. You can block messages from certain users, block messages from people who are not on your contact list, and suppress repeated authorization requests. Optionally, senders of blocked messages can be notified with an auto-reply.
NoxBot is a modular IRC bot that uses the platform independence of PHP. NoxBot is easy to use and features many commands that can be given to the bot over IRC. There are the many available modules. If NoxBot does not provide exactly what you need, then it can be easily implemented as a module. NoxBot tries to stay as RFC-complaint as possible. Some of its features include authentication, module management, a help system, multi-lingual support, timers, a storage system that separates modules, and many more.
Pidgin-paranoia is a plugin for Pidgin (formerly known as Gaim) that provides information-theoretically secure encrypted conversations using one-time pads. Because the plugin uses a one-time pad where the secret key has the same length as the message and the key is only used once, the encryption is information-theoretically secure. This means that from the encrypted messages the contents of the messages are not revealed. In short: If you use truly random numbers to generate the key files, and if you keep them perfectly secret, one-time pads can not be broken.