If you like living on the bleeding edge and can't wait for the latest features and bugfixes, then you can install a development build or build Smuxi from the git source repository.

Installing Development Builds

Debian

On Debian 6.0 (squeeze) you can use the daily APT repository by running:

sudo -s bash -c 'echo "deb http://ppa.launchpad.net/meebey/smuxi-daily/ubuntu lucid main" >> /etc/apt/sources.list'
gpg --keyserver keyserver.ubuntu.com --recv-keys FC6D77D5
gpg --export --armor FC6D77D5 | sudo apt-key add -
sudo apt-get update
sudo apt-get install smuxi

On Debian Testing/Unstable you can use the daily APT repository by running:

sudo -s bash -c 'echo "deb http://ppa.launchpad.net/meebey/smuxi-daily/ubuntu natty main" >> /etc/apt/sources.list'
gpg --keyserver keyserver.ubuntu.com --recv-keys FC6D77D5
gpg --export --armor FC6D77D5 | sudo apt-key add -
sudo apt-get update
sudo apt-get install smuxi

Ubuntu

On Ubuntu you can use the daily APT repository by running:

sudo add-apt-repository ppa:meebey/smuxi-daily
sudo apt-get update
sudo apt-get install smuxi

On Ubuntu Server you can use the daily APT repository by running:

sudo apt-get install python-software-properties
sudo add-apt-repository ppa:meebey/smuxi-daily
sudo apt-get update
sudo apt-get install smuxi

Windows

On Windows it is even simpler and you just need to install a development snapshot which you can find here.

Building Smuxi from Git Source Repository

Debian / Ubuntu

On Debian and Ubuntu it should be as simple as running the following commands:

sudo apt-get build-dep smuxi
sudo apt-get install git
git clone git://git.qnetp.net/smuxi.git
cd smuxi
./autogen.sh
make run

On Ubuntu 11.10 (Oneiric Ocelot) the compiler has to be dmcs using this command:

./autogen.sh MCS=/usr/bin/dmcs

On older Debian systems (like Debian 5.0 / Lenny) you need to install the build dependencies by hand using this command:

sudo apt-get install build-essential pkg-config mono-devel lsb-release gettext intltool libtool autoconf automake autotools-dev