While the pack exists as a standalone download (often found via torrents or archives), it is the standard firmware for several "all-in-one" arcade machines: Pandora Saga Box:

Because the pack is designed for low-power ARM devices, it runs beautifully on these Linux-based handhelds. You simply drag and drop the Roms folder onto the second SD card. Pro tip: Delete the "Arcade" folder if you are on a weaker device to save battery.

The "6666-in-1" ROM pack is a well-known fan-made multicart collection for retro consoles (commonly Genesis/Mega Drive or Famicom/NES variants). It bundles thousands of ROMs — including original titles, hacks, bootlegs, prototypes, and homebrew — into a single image intended for flash carts or emulators. RetroLegends refers here to community releases and pages that catalog or discuss these packs, their contents, and compatibility.