IRC client software 
  AmigaOS IRC Client. 
  Enhanced UNIX Internet Relay Chat client. A small list of supported OSs: Linux, FreeBSD, NetBSD, OpenBSD, Digital UNIX, SunOS, Solaris, HPUX, AIX, UnixWare and BSDi. 
  Truely original and entertaining Microsoft IRC client. 
  Global Chat (tm) IRC client for UNIX and X/Windows, Microsoft Windows and Macintosh. 
  IRC program for the Macintosh. 
  IRC client that runs under most UNIX platforms. 
  IRC client for the Macintosh. 
  IRC client for Windows. 
  Tcl/Tk client for Unix, PCs (Win3.1, Win95, WinNT) and Macs (both PPC and 68k). 
  Client for the Microsoft Windows 3.x, Windows 95 Platforms and Windows NT. 
  IRC client for VM/CMS. 
  IRC client for Unix. 
  Client for 32-bit Windows (95 and NT) and 16-bit Windows. 
  X11 (X Window System) Client for IRC. 
  IRC client available for X Windows. 
These links above leads to the homepage of each client. This way you can be sure to get your hands on the newest versions of these programs along with all the help you might need in order to get it started on your machine.