First you will need to install a few libraries to compile the source

Build tools & libraries:

• Automake, Autoconf, gettext, pkg-config
• Mono SDK (>= 4.6.2)
• Nini (>= 1.1)
• log4net
• SQLite3
• GTK# (>= 2.10) (optional, but required for the GNOME frontend)
• Notify# (optional)
• Indicate# / MessagingMenu# (optional)
• DBus# / NDesk.DBus (optional)
• GtkSpell (optional)
• STFL (optional)

Depending on your operating system and favorite distribution the installation of the listed applications varies. For Debian based distributions it's just a matter of the following commands:

apt-get install mono-devel mono-xbuild libnini-cil-dev liblog4net-cil-dev libgtk2.0-cil-dev libglade2.0-cil-dev libnotify-cil-dev libdbus2.0-cil-dev libdbus2.0-cil-dev lsb-release

./autogen.sh || ./configure
make

make install

Now you can start Smuxi from the GNOME or KDE menu.

This directory contains the source code of all Smuxi components.

This directory contains libraries that Smuxi needs and ships as part of Smuxi.

These directories contain translation files based on gettext.

The debian/ directory contains upstream packaging used for the daily development builds for Ubuntu and Debian found on launchpad (which you can subscribe to via sudo add-apt-repository -y ppa:meebey/smuxi-daily && sudo apt update). The official (downstream) Debian packaging can be found on here.