The Nintendo Power cartridges, with no relation other than the name and Nintendo connection to the American Nintendo Power magazine, were two flash cartridges developed for the Super Famicom and Game Boy in Japan that allowed users to insert the cartridges into a special writing machine and buy new games that could be saved to the internal memory. Unless one very large game was loaded, a menu system would allow for selection between different games on the cartridge. These cartridges released later in the system's lifespans and allowed a cheaper way for Nintendo to distribute new copies of older titles without having to commit to large ROM cartridge runs and new boxes, although manuals were still provided.
The Super Famicom version was introduced in 1997 (after the Nintendo 64 was on sale), with the Game Boy version appearing in March 2000. The system was similar in idea and usage to the Famicom Disk System from the 1980s, allowing a cheaper and re-writable way to get games. The Disk System was contemporary to the Famicom with standard cartridges eclipsing it in the 1990s but these cartridges came towards the end of their system's lifespans and were not as much of an additional hardware add-on.
I found this Super Famicom Nintendo Power cartridge at the retro and import games store near my parents house nine or so years ago. These cartridges were made in Taiwan, unlike earlier Super Famicom games made in Japan. The cartridge is a neat white and stickers from the writing kiosks could have been used to mark what games were on the cartridge. The Nintendo Power logo used for the system is similar to, but not exactly the same as, any of the Nintendo Power magazine logos.
The Super Famicom cartridge has nice funky 16-bit menu music with different instruments coming in and out. Click the image above to see the video of this cartridge booting up and sitting on the title screen for a while.
This service was discontinued in February 2007, years after new titles had stopped coming out... Some games were exclusive to the system and could not be bought on a normal cartridge, including a bunch of volumes of Picross, which is a puzzle game that I really, really like, so I'm glad that this system exists and those games were made!