Dr. Scott M. Baker has a nice write-up about building a multi-ROM cartridge for his Atari 5200 using Raspberry Pi:
The Atari 5200 is a vintage gaming system from the early 1980s. At the time I owned a 2600, but I always wanted a 5200. Well, in 2018 I finally decided to find one on eBay and buy it. I learned that the first thing you want to do after attaining a new gaming console is to get your hands on every available game cartridge for it, so I made this multi-ROM cartridge.
A multi-ROM cartridge, or “MultiCart” is a cartridge that contains more than one ROM image. There are multiple ways to go about this from selector switches to pick the cartridge you want, to built-in in game menu systems. I decided to go the route of using a Raspberry Pi for the user interface, making a WEB UI available to pick which cartridge is used.
The goal is not simply to play retro games on modern hardware — there’s any number of emulation solutions for that. The goal is to play retro games on retro hardware, but use a modern system to load the game image into the console.
Check out the video after the break.