The Bandai Datach Joint ROM System is an add-on for the Nintendo Famicom. It plugs right into the cartridge slot and comes with its own small cartridges. The games are enhanced with barcode cards, similar to the Mattel HyperScan.
The retail package with one include game, Dragon Ball Z: Gekitō Tenkaichi Budokai, is rather easy and cheap to obtain.
Additional games are very rare and even rarer and pricier when the corresponding barcode cards are included. I’ve seen some bootlegs of those games on regular Famicom carts but never tried them so far.
In the 80s Sharp made some interesting devices powered by the Nintendo Famicom/NES technology. The less known devices are the Famicom Titler, a video subtitler, and the C1 NES TV/Sharp Nintendo Television, a television set. More common is the Twin Famicom, a console that plays Famicom cartridges and Famicom Disk System Disk Cards (and, with a 72-to-60-pin adaptor, NES cartridges too). This is the black Turbo version AN-505-BK: