Miranda IM is a multi protocol instant messenger client for Windows. Miranda IM uses very little memory and is extremely fast. It supports ICQ, AIM, MSN, Jabber, Yahoo, IRC and more. Functionality can be greatly enhanced with an extensive set of plugins (currently over 350) as well. The interface and setup is a bit more involved than other IM clients like Portable Gaim, but the customization options available are richer.

Portability Note: Miranda IM itself is actually portable without modification. It will be slightly larger (1MB vs 2MB) and will keep the settings in the base directory unless you alter the INI files. Portable Miranda IM is made available mainly for the convenience of users of other portable apps as it allows the same directory structures without modification or configuration changes.