What is CRX format?

CRX format is chrome extension format that is used by the Chrome WebStore toinstall extensions in chrome webbrowser.

CRX is downloaded from webstore to chrome, which then reads it and install it's contents on Chrome WebBrowser.

It's just a rename of zip file, so it does not have any special reader. And well known WinRAR is enough to read it afer renaming it to a zip file.