Because I searched for it now for half an hour and could only find it in the Google cache.

Irssi proxy usage:

First you’ll need to have the proxy module installed, either configure
irssi with –with-proxy and do make install, or manually:

cd src/irc/proxy
make
mkdir ~/.irssi/modules
cp .libs/libproxy.so ~/.irssi/modules/

In irssi, say:

/LOAD proxy

You really should set some password for the proxy with:

/SET irssiproxy_password secret

Then you’ll need to configure the ports/ircnets the proxy listens in, something like:

/SET irssiproxy_ports ircnet=2777 efnet=2778 freenode=2779

There we have 3 different irc networks answering in 3 ports. Note that you’ll have to make the correct /IRCNET ADD and /SERVER ADD commands to make it work properly.