uhub is a high performance peer-to-peer hub for the ADC network. Its low memory footprint allows it to handle several thousand users on high-end servers, or a small private hub on embedded hardware. It uses the ADC protocol, and is compatible with DC++, jUCy, and other ADC clients.
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.
JTelIRC is an advanced IRC framework for Java. It is mainly intended for writing automated clients ("bots"), but may be used for normal clients as well. It provides an intuitive and well documented Java interface to IRC and makes it extremely easy to write advanced clients quickly.