Kandan is a free open source chat application built Ruby on Rails (A popular ruby language framework) and supports many databases.

Kandan has really cool features and beautiful interface. It enables to manage multiple chat rooms simultaneously, easily share images, youtube links, etc.

• Searchable Message History
• File Uploads
• Multiple Chat Room Management
• Shared Room Audio
• Easy deploy to with CloudFoundry, Heroku, dotCloud, etc.
• Collaborative Team Chat
• Unlimited Channels

Balloons.IO is a web-based, realtime, open source multi-room chat server and client.

Balloons chat application is built by combining the latest technologies in web design and development such as CSS3, HTML5, Node.JS, and Redis.IO Socket.IO.

What counts is the experience of the user, and Balloons has a robust flexible backend with nice and functional designs. This realtime chat application uses easy-OAuth for authentication with Twitter.

Candy is an open source multi-user JavaScript chat client for Jabber with beautiful default theme. It lets you join multiple rooms, start private conversations and get notified when new messages arrive.

This JavaScript chat client ignores spammers, lets you kick / ban users and change the subject of the room.

Features

• Focused on real-time multi-user chatting
• Easy to configure, easy to run, easy to use
• 100% well-documented JavaScript source code
• Built for Jabber (XMPP), using famous technologies
• Used and approved in a productive environment with up to 400 concurrent users

AJAX Chat is a fully customizable open source web chat software implemented in JavaScript, PHP and MySQL.

AJAX Chat supports voice chat that is powered by Flash & Ruby (sound support is optional).

Features

• Multi-lingual chat software
• Realtime monitoring and logs viewer
• Custom emoticons support
• Multiple channels & private messaging

Ajax Chat is developed with security in mind and it is strong against code injections, SQL injections, cross-site scripting (XSS), session stealing and other attacks.