Spark - Free Open Source Crossplatform IM Client for Business and Organizations

Spark is free, secure, fast, Open Source, cross-platform IM client optimized for businesses and organizations. It features built-in support for group chat, telephony integration, and powerful security. It also offers a outstanding end-user experience with features like in-line spell checking, group chat room bookmarks, and tabbed conversations.

Spark, based on the open IETF standard XMPP (Jabber) protocol is a cross-platform, Java-based Client optimized for use with Jive Software's Open-Source XMPP Wildfire Server.
The Spark API provides a framework for adding extensions on top of the protocol and/or UI of the Spark client. For example, you could write your own message filter or add a button to a chat room and send files using the File Transfer API.

Combined with the Openfire server, Spark is the easiest and best alternative to using un-secure public IM networks. Sparkplugs dynamically extend the features of the Spark instant messaging client. Use Sparkplugs to customize Spark for your business or organization or to add an innovative twist to instant messaging.

Features

Spark features such as Chat, IM, Voice Chat, conference room, spellcheck, ChatManager, SparkManager, Ability to add your own XMPP functions using the SMACK API, SoundManager, Event Handlers, ChatRoomListener, File transfers, ContactListListener, MessageListener, PresenceListener, ContextMenuListener, ContactItemHandler, SessionManager,Components, GaduGadu, IRC, and SIMPLE transports now supported, avatar, note editor, etc.

Download Spark

Spark is support for Windows ,Linux, and Mac OS. This is freeware.