Applications that can open APPCACHE files include web browsers such as Google Chrome, Safari, and Firefox.
APPCACHE File Format - More Information
APPCACHE files are simple text files, providing offline access to web pages for running without an internet connection. The presence of APPCACHE designates a page as available offline.
How to Reference an APPCACHE file?
In your HTML page, an APPCACHE file is referenced as follow.