Pidgin : https://pidgin.im/

Pidgin (formerly named Gaim) : https://en.wikipedia.org/wiki/Pidgin_(software)

Weechat[0], previously Irssi

[0] https://weechat.org/

Colloquy - https://github.com/colloquy/colloquy

Konversation: https://konversation.kde.org/

telnet