Free Communication & Chat Software

Digsby
This handy tool lets you chat with your contacts over multiple instant-messaging services (including Windows Live Messenger, Yahoo, AIM and ICQ), check for new email and keep track of what your friends are up to on MySpace, Facebook, Twitter and LinkedIn. Conversations are managed in tabs although you can drag them out into separate windows if you prefer. During the installation process you will be prompted to install other bundled software. Make sure you click the Decline button each time, unless you want these extra programs.
Minimum requirements: Windows XP/Vista or Mac
File size: 4.3MB
Download: Digsby

Thunderbird 3 Beta 1 Preview
Mozilla Messaging recently released a preview beta of the next version of its popular email program. New features include a tabbed interface for email, a tweaked message reader view and an improved add-ons manager. The program now also makes use of Gecko 1.9, Mozilla’s latest layout engine. Subsequent releases should see the inclusion of a built-in calendar, bringing it a little closer to Outlook in terms of features.
Minimum requirements: Windows XP/Vista or Mac
File size: 7.9MB
Download: Thunderbird 3 Beta 1 Preview

Yahoo Messenger 9
Yahoo's chat client lets you import contacts from 20 different services, including Google Mail and Hotmail/MSN. In addition to instant messaging your friends you can chat to them by VoIP or video, and take part in multiplayer games. The tool also includes an inline video and picture viewer for displaying media directly in the chat window. The latest version introduces Pingbox, a handy application that lets you embed Messenger on any blog, website or social-networking page, so that people can message you directly. Minimum requirements: Windows XP/Vista
File size: 421KB (installer)
Download: Yahoo Messenger 9

Skype 4.0 beta 3
The forthcoming release of the popular VoIP service boasts a new, larger interface (although you can switch to a compact view if you prefer), with the emphasis on video chat. Message alerts now appear in the Windows Taskbar, System Tray and the program itself, making them impossible to miss. Skype 4.0 also comes with a Firefox extension, letting you call numbers on any site with just one click.
Minimum requirements: Windows XP/Vista
File size: 23.8MB
Download: Skype 4.0 beta 3

Pidgin 2.5.2
Originally called Gaim, this handy instant messenger client lets you log in to multiple accounts across several IM networks simultaneously. It’s compatible with Windows Live Messenger, Yahoo, AIM, ICQ, Jabber (including Google Talk) and IRC among others (you’ll need to have an account set up on the different services to use them, of course). The software supports plug-ins and comes with 25 ready to enable.
Minimum requirements: Windows XP/Vista
File size: 12.5MB
Download: Pidgin 2.5.2