icqlib is the most feature complete, open source, library implementation of Mirabilis' ICQ protocol available on the Internet. It currently supports most of the ICQ UDP v5 and ICQ TCP v2 protocols, including new UIN registration, chat, and file transfer. It was written in C for portability, and supports multiple simultaneous connections to ICQ servers, SOCKS5 firewalls for both UDP and TCP protocols, an event-driven, non-blocking interface, and the Russian language (automatically performs conversion from Windows 1251 encoding to Unix koi8 encoding).
The Off-the-Record (OTR) Messaging proxy is a multi- platform proxy that allows you to have private conversations using the AIM client of your choice. It provides encryption, which prevents someone who intercepts your instant messages from reading them, authentication, which ensures that the correspondent is who you think it is, and perfect forward secrecy, which ensures that no previous conversation is compromised if you lose control of your private keys.
Twisted Words provides implementations of a handful of IM protocols, including IRC, MSNP8, OSCAR, TOC, and Jabber. It also comes with a multi-protocol server built around a few simple interfaces, the goal of which is to facilitate implementations of novel servers, clients, and bots. Out of the box, it comes with server that accepts connections over IRC and PB and seeks out installed third-party plugins to support other interfaces (for example, a Nevow LivePage-based Web interface).
JClaim is an instant message client, tools, and development framework. It supports AIM, ICQ, Yahoo!, MSN, Jabber, Google Talk, and SMS. The framework can be used for designing your own tools. The UI includes spell checking and a lot more. A Web interface is included for remote access.
JabberTools is a set of console and Web-based Perl tools depending on Net::Jabber that makes it easier to use Jabber and convert to using Jabber from other instant messaging systems (e.g., AOL and ICQ). The tools include a Jabber account manager and an importer that converts your previous contact lists/rosters/buddy lists into your Jabber roster.