The Video Lan Client is a video player that hadles just about any codec. It is also cross platform, with versions available for Windows, OS X, and several versions of Linux.
Mozilla Firefox is the Internet's fastest growing browser. It is an open-source project by the Mozilla Corporation, aimed at providing a minimalist and refined browser capable of accepting a wide variety of add-ons.
Mozilla Thunderbird is a popular alternative to Microsoft's Outlook and Outlook Express. Its security is better than's Microsoft's offerings
Gaim is an IM client that works with multiple networks including AIM, MSN, Yahoo, and Jabber, provided you have an account for each
Skype is a popular voice over ip appplication that allows users to place calls over the Internet to other Internet users or a regular phone line.