24im is a free hosted group collaboration service. 24im is built for any group, small or medium sized business, and is hosted on fast and reliable servers. 24im is a smarter, faster, easier way to deliver enterprise-grade IM to your private group. For Free. Features:

• Enterprise Instant Messaging
• Ticker broadcast system
• Project management
• Searchable history and logs
• Livechat Support/Sales system
• Guest user access
• Broadcast messaging
• Offline messaging
• Group activity feed
• File storage and sharing
• Web-based or desktop access
• Role based administration

Free and Requires Windows 2000, XP, Vista, or 2003 Server. Also requires an active account.