Often we need to make large files smaller, using a file compression program such as WinZip or WinRAR is typical. Those programs can compress files with the file format .zip, .rar, etc. However, both these products are shareware and come at a cost if you want the full versions. But there is something better, it's open source and doesn't cost a penny! It is called 7-Zip, it supports the popular .zip and .rar formats, it also has its own .7z format which I've found to be much better than the traditional .zip format. Often compressing using .7z means a very much smaller file than when using traditional .zip.
I've been using 7-Zip for a couple of years now and I am very happy with it. The interface is simple, not as glossy as WinZip's - it may turn you off but spend some time with it, you'll get used to it soon enough.
The best thing about 7-Zip is that there are tools for the power user or for those who need to script. For example, there's a command line version included and you can make self-extracting archives that can automatically run exe files after extraction.
7-Zip is another example of a truly excellent open source project. There are lots of add-ons to use it with other software, such as Firefox or FAR Manager, etc. It's an active project, new versions are available often.
Find out more here: www.7-zip.org
My rating: 9/10, highly recommended