Kiwi IRC - A hand-crafted IRC client that you can enjoy. Designed to be used easily and freely.
PuTTY - Popular free terminal application. Mostly used as an SSH client.
Colloquy - Traditionally, chat clients on the Mac have been anything but glamorous.
MobaXterm - Enhanced terminal for Windows with X11 server, tabbed SSH client, network tools and much more
Terminal on FB Messenger - Take control of your terminal through Facebook Messenger
iTerm2 - A terminal emulator for macOS that does amazing things.