Xante carts are my most sought after 2600 collectible. I have none in my personal collection, and might never, as these generally go for thousands of dollars when then happen to pop up for sale (which is not very often). While not the *most rare* of 2600 carts, they are pretty dang close. To me, Xante carts are the most collectible because they actually went into production (the kiosks! the kiosks!) and are not simply prototypes. They had a short run, but they were legit parts of the “in circulation” games for Atari 2600 . Below are some images of Xante’s release of Demon Attack (bought at a kiosk in K-Mart).