License: Open Source/GPLv3
Description: A cross-platform instant messaging client with a built-in whiteboard, VoIP support, file transfer, and so forth.
Other: You can make a cross-platform USB stick. Simply put the Windows, Mac OS X and Linux binaries on the USB stick. Open the binary on all platforms and open the preferences screen. In the first settings panel you'll find a setting to store the preferences in the same location as the binary. After you do this, settings and chat history will be stored on the USB stick and will be available on whatever platform you use the stick.