Free messages, Free Calls. Unlimited!
Nimbuzz Messenger combines the power of internet and smart phone messenger into one, and lets you make cheap international voice calls, send unlimited chat messages, share files on any mobile device across popular messengers. Nimbuzz Messenger is available on Android, iOS, Blackberry, Symbian, Java, Windows and Mac.

A lightweight XMPP client based on the Smack framework.

Yaaic (Yet Another Android IRC Client) is an Internet Relay Chat (IRC) client for Android devices.