If you aren’t in the know, @Wildman_Fujiami made a private server to revive YMSG, the protocol used to power the (legacy) Yahoo Messenger clients. Currently, it only supports version 6.0 of the client, but there’s probably more to come. Just follow the instructions here: How to patch Yahoo! Messenger 6.0.0, type in some credentials (without even registering 
), and you’re in.
Also, some insight, @valtron, I, and presumably the rest of the Escargot team are currently implementing YMSG on Escargot, and plan to start with YMSG9/10 (clients 5.0-5.5) and beyond. So be sure to check in that department. 
EDIT: Yahoo! Messenger is still being maintained by Yahoo! themselves, except that they killed ALL of the working legacy versions off (the last one being Yahoo! Messenger 11), and the new versions, in my opinion, aren’t the best. Not just in UI, but also in functioning correctly (e.g. They killed off contact notifications to notify a user when their contacts have gone online. Why in their right minds would they do that???).