Pidgin Portable

This is the portable version of Pidgin - the instant messaging service that is compatible with AIM, Google Talk, ICQ, MSN, XMPP, Yahoo and others.
Since this is a portable product, Pidgin does not need any installation, so your Windows registry entries do not change. You can also place the software on an external drive and run it directly from there.
Why would you choose Pidgin? In case you share your computer with multiple users who have accounts on different instant messaging protocols, then you need Pidgin to provide you with access to all of them.
Pidgin's user interface is very clean - it combines all the necessary elements that make an instant messenger look good, so graphics do not stop you from having a decent workflow.
The program has a lot of interesting and practical plugins that improve its abilities once you enable them, such as Conversation Colors (customizes colors in the conversation window), History (shows recently logged conversations in new conversations) and Auto Accept (applies to file transfer requests from selected users).
Furthermore, you can customize conversations (e.g. enable buddy icon animation, use smooth-scrolling, use font from theme), smiley themes, sounds, networks and status/idle, but you can also use the Buddy Pounce option to automatically perform actions (open an IM window, pop up a notification, send a message, execute a command, play a sound), when a buddy sends a message, signs on etc.
Pidgin uses a significantly less amount of system resources than other instant messengers, and it worked flawlessly during our tests. Bearing this in mind, we strongly recommend you Portable Pidgin.

Pidgin Video Guide