Wallops is a light-weight IRC client with an emphasis on compatibility. It runs on Macs where ShadowIRC or Ircle won't, namely oldies like a Mac Plus. It does, however, also run fine on Mac OS 9 machines. Version 2.0 now comes with a lot of changes, including (finally!) resizable windows, tabs and additional commands. Find the full changelog and download at the author's website.

Edit. Version 2.1 has since been released, containing a couple of bugfixes and enhancements.

M9L's user MigMac pointed out the work that Ed Mendelson has lately been doing on his MacOS9 App. While it's basically just good ol' SheepShaver (the OS 9 emulator), Ed went to great length to reduce incompatibilities and to improve stability. It also minimizes the emulation setup process. Check out this thread in our forum for more info.