ICQ: 20 Years Is No Limit
Around 2000 I got annoyed with the ads and crap in ICQ, so I wrote Miranda ICQ, now called Miranda IM (http://www.miranda-im.org/) based on libicq. One of my main inspirations to write the app was I wanted to connect a chatbot to ICQ to harass my friends, but the standard API wouldn't allow sending messages. So I added a plugin API, connected the MegaHAL chatbot and good times ensued.I lost interest in Miranda shortly after that, but I'm always impressed that a group has kept it going.