At times I have to face this question as What is available in Open Source World. People who dont know much about Open source ask what kind of Softwares I can find there? Initially when it all started there were not many softwares available as Open Source but today we have whole bunch of softwares available as open source.
Linux : Does not need any introduction.
JNode : A Java based Operating system. This is a work in progress and once completed will run the JVM upon boot. More information can be found at http://www.jnode.org/
Star Office: One of the best alternative to Clumsy MS-Office. More information can be found at http://www.staroffice.org/
Eclipse : One of the Best Java IDE available today. Check it out at http://www.eclipse.org/
Free Pascal: The Pascal Compiler for Cross-Platform development. Visit http://freepascal.org/
Lazarus: The Open Source Delphi IDE Check it out at http://www.lazarus.org/
MySQL : One of the best RDBMS available today. Check it out at http://www.mysql.com/
JBoss and TomCat are two most famous Application Servers in Developer Community.
DVDShrink is one of the utility to copy DVDs. Check it out at http://www.dvdshrink.com/
This is not the comprehensive list of Softwares available in this world. The list is very long and there are couple of sites which has lots of Open Source projects for one to look at and start participating. One such site is SourceForge.net.
Have a good time in the World of Open Source :) There is more for you to take from here than you can carry.
Until Next Time..:)