Open Source Software

It has been some time since I had begun to admire open source software and their capabilities, where anybody can start right away and get their technical ideas implemented and where there exists a free software corresponding to almost every commercial software, there may be (except video games).
While working on windows operating system, most of the software has to be paid for to be able to use it and if one wants to be economical or has not much funding, then it is indeed difficult to get done with your work.

Various compression software are available and most of the commercial ones are being used, mostly, unless working in a non-windows environment, cuz otherwise a simple zip/gzip and tar -c commands would do to zip and archive the file(s).
Generally one may have scruples while using a pirated copy of a commercial software. Normally it's not the case :), but it is always good to respect someone's work, especially when you find the software useful enough for you. So, if you can't buy the software, you falter to use it (if not, you should). 7 zip to the rescue! It's by far the best compression software I have used and always use at home and would any day recommend it to everyone. Its interface is fairly user-friendly, compression algorithm is more efficient in terms of compression, although it does take some time depending on the system processor one has under the hood.
It also is capable of splitting compressed file into numerous files of size given by the user, which can later on be extracted into the original file, with as much ease as extracting a single compressed file. This is particularly useful, as I have found it to be, while mailing using Microsoft Outlook at office, due to the file size limitation of the attachments.
It can be freely downloaded from here. Do contribute if you can, as donations do help developers.

Another software, open source, of course, which I use for audio editing is Audacity. The word itself is a link, so please do visit its homepage to get to know more about the software, although you may find a gist below. :)
Firstly, the software is free. Can be used for audio editing, enhancing, amplification, bass-boost, fade in-fade out and so many more such effects that audio enthusiasts would love. Any supported audio file can be edited to the precision of a 100000th of a second. :) Cool, ain't it? Finally the file can be exported to one of mp3/wav/ogg audio formats.
All in all, a cool editing software to have and its FREE of cost, of restrictions and to modify ;)!

For all the graphics enthusiasts out there, or rather those interested in game coding and looking for a game engine, then what's better to begin with than Irrlicht! This engine has already been used to develop a few pretty good games with decent graphics and is being actively upgraded.
The best part of an open source game engine, or any open source software for that matter, is that a developer can customize it to her/his advantage.

Basically there will be numerous open source software, commercial implementations of which we may be using in our daily life, without giving the developers their due. Most software and their developers do need credit. Hence if buying a software is not an option, look for a corresponding open source software and do donate (money :)) even if it is the smallest of amounts, to the free software you find useful.