What's the most useful open source or free software available??

I think best open source software available is without a doubt Mozilla Firefox. The mozilla have changed the way browsers used to be.

I think Open Office and PDF reader are the most used and useful softwares available. I dont think i need to write anything about acrobat PDF reader. It used by almost everyone. Then about open office . It is just like microsoft office with only difference that it is open source. This product by Sun microsstem is availabe for free download. It has all the capabilities of microsoft office. With advvantage that it can suppoet all MS-Office formats so need to worry about formats also. You can make it save all ms-office files.

In the internet world I would say Mozilla Firefox is the most widely used and popular open source browser. Open Office I guest would follow suite.

I think SpyBot is the best freeware software.It is an antispyware software, plus it has a start up manager, registry checker process list and a lot of other cool features.

try portable apps, it is simple

i think firefox is the best one. it has a lot addon that really helpful