Ircii

The ircII program is a much improved IRC client. As of 2009 the ircII-4.4 client can connect to almost all 'modern' IRC servers, however this version is lacking SSL support which can be found in newer releases... However it's unlikely that such software would compile on ancient platforms like 4.3 BSD.

I can certainly verify that it works on the server chat.taucher.net

It can be downloaded from here. I have found that a good ANSI compiler (gcc 2.x) is needed to build this.