I think winrar,
http://download.cnet.com/WinRAR-64-b...-10965579.html, is likely still the most common. You can just never donate or whatever and use it for free.
.zip files are very, very common though so I'm just simply surprised you're not familiar with them at all. But maybe you were able to unzip it fine anyway since it seems you were able to get some games into the database?
Paying for something would at least provide you with a user guide most likely and/or youtube videos of how to do things. But, yeah, the route your going makes the most sense unless you want to illegally obtain paid stuff.