A client is what one uses to make use of the Tox core.
Here is a list of clients available for testing and developing, you can click an image to zoom in:
A deprecated ncurses-based CLI, bundled with the core. First client, initially made by astonex.
The second ncurses-based CLI bundled (was in the core repository, once in its own). Initially made by plutooo. Supersedes nTox.
A Vala/Gtk+ graphical user interface for Tox, written by naxuroqa.
The first GUI written in Qt. Initially written by nurupo.
The second GUI, written for OSX and Windows. Unstable, initially written by stal.
The third GUI, written for OSX. Very unstable, written by dparnell.
The fourth GUI, written for iOS. Limited in features, written by JmanGuy.
Written in Qt/QML, this GUI for Tox is by Alek900.