Pidgin
Open Source
Pidgin is a free and open-source chat client which supports AIM, Google Talk, ICQ, XMPP protocols.
mIRC
Commercial
mIRC is an Internet Relay Chat (IRC) client for Windows.
KVIrc
Open Source
KVIrc is a graphical IRC client for Linux, Unix, Mac OS and Windows.
AdiIRC
Free
AdiIRC is a free Internet Relay Chat (IRC) client.
Chatzilla
Open Source
ChatZilla is an IRC client for Mozilla-based browsers such as Firefox.
HexChat
Open Source
HexChat is an open-source, cross-platform IRC client.
Quassel IRC
Open Source
Quassel IRC, or Quassel, is a graphical, distributed, cross-platform IRC client.
Smuxi
Open Source
Smuxi is a cross-platform IRC client for the GNOME desktop inspired by Irssi.
X-Chat 2 for Windows
Free
X-Chat 2 for Windows is an unofficial open-source GPL X-Chat (UNIX IRC client) build for Windows.
LimeChat
Open Source
LimeChat is an IRC client for Mac OS X.
Compare Textual with alternatives
Compare Quassel IRC and Textual and decide which is most suitable for you.
Compare X-Chat 2 for Windows and Textual and decide which is most suitable for you.