Image: YouTube (smackedsam)
It's not an official product, naturally. But this homebrew unit does at least look like a Dreamcast unit, and it plays plenty of Dreamcast games to boot.
The mini Dreamcast is the work of YouTuber smackedsam, who put a stock Raspberry Pi3 with some modded ports into a shell that looks like a Dreamcast.
The retro box has four ports for wired controllers and has 15 games loaded, including Power Stone, Soul Calibur and Dino Crisis. Not everything runs at a buttery smooth frame rate - the emulation settings are turned down to the lowest - although smackedsam notes that you could overclock the Pi3 and house the unit in a shell with some cooling and fans for better performance.
He'll apparently be selling Dreamcast Mini Legendary shells and Dreamcast Mini units in the future, something I can't imagine SEGA will permit for too long. Nonetheless, it's neat to see what a Dreamcast Mini could look like. Surely someone at SEGA's thinking about it.
If you're having troubles or need advice on how to get the Dreamcast going with Retropie, there's a useful video guide here.