Psi is a free instant messaging application designed for the XMPP network (including Google Talk). Fast and lightweight, Psi is fully open-source and compatible with Windows, Linux, and Mac OS X.
License: Open Source
Disa is a versatile messaging app that prioritizes user privacy and customizable interfaces, making it ideal for personal use and smaller groups. Conversely, Psi is more suited for professional environments, offering robust protocol support and extensive community features, but it can be less user-friendly for casual users.