Downloading ShadowIRC 1.1 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. The software belongs to Communication Tools. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe.
From the developer:
ShadowIRC is a fast IRC client for the Mac OS. The program is extensible with C-coded plug-ins compiled with CodeWarrior. This makes ShadowIRC plug-ins faster and more flexible than AppleScript-based scripts, though you will need knowledge of C and a copy of CodeWarrior if you are going to write plug-ins. Among other features, ShadowIRC can process Ircle and mIRC color codes (though not at the same time). The source code is also available.
You may want to check out more software for Mac, such as TRx Recorder or Skype2Prowl, which might be related to ShadowIRC.