An “index of” page is a simple, unstyled directory listing generated by a web server when no default file (like index.html ) is present. In the early web, these were common—a raw, transparent view of a server’s file structure. Today, they’re often accidental, but some are intentionally left open for file sharing.
The legality of ROM indices is a complex "gray area" with significant enforcement from copyright holders. iNES file format - Software Fundamentals index of nes roms
These files are often hosted on legitimate developer sites or GitHub, not raw "index of" directories. An “index of” page is a simple, unstyled