free, distributed and user-friendly IRC / Twitter / XMPP / Campfire / JabbR client for Linux, Windows and Mac OS X based on GNOME / GTK+

If you can't get gTalk/XMPP to work then you probably have 2 factor authentication enabled (where you get a SMS with a code). In this case you need to create a special password for Smuxi. For more details check this Google support page.