Memory cards are something we don't really need anymore. The switch uses SD cards, but there are universal storage items that can be used on computers, phones and other hardware. No, the days of dedicated memory card drives are long gone. But when we used memory cards, the coolest of them was probably the VMU devices for Dreamcast.
Part memory card, partial screen accessory, VMU was also a mini game console with its own small library of mini games. It wasn't perfect but it was such a cool idea.
The retro-focused YouTube channel, Stop Skeletons From Fighting, released a fantastic video covering all the cool and weird things you can do with a VMU.
For example, did you know that you could actually play Silent Scope on a VMU? Not only can you do it, but you can also play it with the Dreamcast mouse. This is not the best way to play Silent Scope but it is the silliest way to play. Virtua Tennis a game that you can play with a fishing rod ( really ), can also be played entirely on a VMU. When connected to a controller, VMU displays a wireframe representation of the game. Again, not the best way to play Virtua Tennis but perhaps the strangest way.
Most games did not have such wild VMU features. In fact, many games on Dreamcast only showed the logo of the game. Other games included useful information, such as Resident Evil 2. When you play RE2 VMU shows you how much ammo you have and your health status.
VMU was not perfect. It didn't have much storage space, a problem for a memory card. It was also more difficult to find clock batteries and was prone to bugs and other problems. But still, the idea of a portable mini-game console that was also a memory card is such a crazy and ridiculous idea that only in the late 90's would SEGA try.
If you still have a VMU, people are creating homebrew software and apps for the small devices. Fans have also created VMU emulators, which allows everyone to move around with some of the mini games that developers created for VMU.