On December 15, 2017, some six months after killing off AIM multi-user chat, Verizon/Oath took the entire AIM service out behind the barn and put a bullet in its head. It's dead, kaput, finis, gone, terminated with extreme prejudice. It has ceased to be. It is no more. Bereft of life, it rests in peace. It has rung up the heavenly curtain and joined the choir invisible. It is an ex-service.
It will not be replaced by anything. It is just dead as a doornail. Period.
But Barflies are nothing if not resourceful! Pending the more complete alternative Scott Bragg is working on, there is an interim replacement bar chat powered by ejabberd running at jabber.caerllewys.net. This server is now fully secured with a 4Kbit SSL certificate.
You will need an XMPP-capable client such as Pidgin, Adium or Miranda, and an XMPP account to connect to it. I have now verified that you should be able to connect to chat.caerllewys.net using ANY valid XMPP account from a properly configured service — Google Talk, for instance. (Not, however, LJTalk. I'm told LiveJournal did something on their servers that makes LJTalk accounts unable to connect to non-LiveJournal XMPP servers. Presumably they accidentally, or maybe intentionally, broke federation.)
XMPP.org has a list of XMPP clients here. There is also a very lightweight pure-Java client at JBother.org, which allegedly should run on anything with Java 1.4.x or later installed. If you're using Miranda, Douglas King has put together a complete tutorial here (Flash required, unfortunately).
(Some clients, Trillian v2.x for example, may call the protocol Jabber instead of XMPP. But it's the same thing. Jabber is just an older name for it.)
Again, these example instructions are for Pidgin, but other XMPP clients should be generally similar. The example at right shows connecting with Pidgin using a Google Talk account.
If you don't already have an XMPP account, or for some reason you cannot connect with the account you have, you can register a new account at jabber.caerllewys.net in any XMPP-enabled client. This example is for Pidgin; Adium should be almost exactly the same; other clients should be generally similar.
The Trillian online manual has instructions here for setting up a Jabber/XMPP account. That manual is apparently for Trillian 2.x; Trillian 3.x should presumably be similar.
Discord has become a popular chat client, and many Barflies have moved there. If you are still in love with Pidgin, however, there is a way to hook Pidgin into Discord, and it is fairly easy.
You need to have a Discord account set up. If you don't already have one, you'll need to do this on discord.com in your web browser. Make sure you have a record of your username, email address, and password. Discord will send you a verification email to activate the account.
You will need to install the purple-discord plugin for Pidgin. Make sure you are updated to Pidgin 2.14.1 before you start.
On Fedora Linux you can install from the main Fedora repository:
dnf install purple-discord pidgin-discord
On CentOS, you can do the same using yum instead of dnf, but will need to add Fedora's EPEL7 repository first.
On Gentoo Linux, you'll need to download purple-discord-9999.ebuild and either extract it to /usr/local/portage/x11-plugins/purple-discord, or create a local overlay for it. (EionRobb has not published an overlay.) There are instructions on EionRobb's Github page if you don't know the necessary steps to do this yourself. Merge the package as normal. Remember that you'll have to flag it as an accepted unstable package.
If using Windows, download libdiscord.dll and libjson-glib. Copy libjson-glib.dll to C:\Program Files\Pidgin on 32-bit Windows, or to C:\Program Files (x86)\Pidgin on 64-bit Windows. Copy libdiscord.dll to C:\Program Files\Pidgin\Plugins or C:\Program Files (x86)\Pidgin\Plugins as appropriate. Remember that you'll have to unzip any zipped downloads.
(Thanks to Monika Beeman for guinea-pigging and documenting the Windows setup.)
Once you have the Discord plugin installed and have restarted Pidgin, go to Accounts -> Manage Accounts -> Add, and create a new account using the Discord protocol. Make sure to select Always Remember password.
If you're seeing repeated Join/Part messages from people with flapping connections, AND you're using Windows, here's how to suppress the messages:
Pidgin 2.6.1 on Windows appears to have a bug that affects creating XMPP accounts. If you use Pidgin on Windows, it is older than 2.6.2, and you don't have an existing XMPP account that you can use, consider upgrading Pidgin and rebooting Windows before trying to create one. (If you don't reboot, the old Pidgin DLLs will still be in memory, and will screw you up, because Windows is too stupid to reload the newer versions without a reboot.)
Pidgin 2 does not support CAPTCHAs for registration verification, and Pidgin 3 has not yet been released. Unfortunately I have to choose between keeping CAPTCHAs turned on, or having a flood of spambot registrations. If you're unable to register an account, but you can get a message to me via another barfly, I can temporarily turn off CAPTCHAs or register your account for you with a temporary password.
If you're using bitlbee with its built-in jabber support, try the following set of commands:
chat add [YOUR ACCOUNT ID] firstname.lastname@example.org
If you're using bitlbee and libpurple, you need this additional command FIRST:
acc jabber set connect_server talk.google.com
(Thanks to Kent Ritchie for documenting the bitlbee setup.)
If you're still using Gaim, it does not support XMPP at all. In this case I recommend you first upgrade to Pidgin, start Pidgin once and close it, then — BEFORE you set up your XMPP account — find your Gaim and Pidgin preferences directories (they will be named .gaim and .purple) and copy the two files accounts.xml and blist.xml from the .gaim directory to the .purple directory. These files contain all of your existing account and buddy information, and copying them over (and making sure you can connect to your existing accounts from Pidgin) BEFORE you add any new accounts will save you a lot of trouble later.