openSUSE 11.0 users can install Smuxi by using this 1-Click install:

Debian/Stable users can install Smuxi from the www.backports.org repository, just add the
following line to your /etc/apt/source.list file:
deb http://www.backports.org/debian lenny-backports main
After that run:
apt-get update
apt-get -t lenny-backports install smuxi
Now you can start Smuxi from the GNOME or KDE menu.
Debian/Testing and Debian/Unstable users can install Smuxi from the official Debian repository, just run the following command:
apt-get install smuxi
Now you can start Smuxi from the GNOME or KDE menu.
In case the official repositories from above are not providing the latest Smuxi version yet, you can use these instead:
For Debian/Testing and Debian/Unstable add the following line to your /etc/apt/source.list file:
deb http://debian.meebey.net/sid/smuxi /
For Debian/Stable add the following line to your /etc/apt/source.list file:
deb http://debian.meebey.net/lenny-backports/smuxi /
After that run:
apt-get update
apt-get install smuxi
Now you can start Smuxi from the GNOME or KDE menu.
NOTE: Ubuntu/Jaunty (9.04) contains Smuxi 0.6.3 and Ubuntu/Karmic (9.10) contains Smuxi 0.6.4.1, but it's recommended to use 0.7 instead!
Ubuntu/Jaunty (9.04) and Ubuntu/Karmic (9.10) users can install Smuxi from this PPA, just add the
following line to your /etc/apt/source.list file:
deb http://ppa.launchpad.net/meebey/ppa/ubuntu jaunty main
or
deb http://ppa.launchpad.net/meebey/ppa/ubuntu karmic main
After that run:
sudo aptitude update
sudo aptitude install smuxi
Now you can start Smuxi from the GNOME or KDE menu.
Gentoo users that are using ~amd64 or ~x86 can install Smuxi by running:
emerge smuxi
Now you can start Smuxi from the GNOME or KDE menu.
Smuxi is in AUR, so just run the following comand to install it:
sudo yaourt -S smuxi
Now you can start Smuxi from the GNOME or KDE menu.
Download: smuxi-0.7.1-1-bin.tar.gz
This package contains pre-compiled Smuxi binaries plus the required
libraries (log4net, Nini, SmartIrc4net), suitable for Linux (using
Mono) users.
Linux users using the binary tarball have to make sure the required runtime and libraries are installed in order to run Smuxi correctly!
You need the Mono runtime (>= 1.2.6) and the GTK# libraries (>= 2.8) which you can download here:
http://www.go-mono.com/mono-downloads/download.html
Alternatively you can install Mono and GTK# from your package repository of your Linux Distribution, just make sure they are the right version!
After you have installed those you can run the smuxi-frontend-gnome script from the binary tarball or run the following from a terminal:
mono smuxi-frontend-gnome.exe
This tarball contains only the source code of Smuxi and is intended for package maintainers of Unix-like operating systems as it requires you to compile Smuxi and the needed components yourself.