Old Gameboys are available aplenty on eBay, Craigslist, and maybe that old box in your mom's garage, but for some people, there's something special about a device crafted with one's own hands. If you fall into that category (and often wax poetic about your ol' Gameboy), Adafruit has introduced a project right up your alley.
Adafruit has released a long write-up detailing how to make your own Gameboy (they call it a "Gamegirl" for obvious reasons) using Raspberry Pi, an SNES controller, and some other easy-to-acquire parts. As you might have guessed, the system runs an emulator, eschewing the need for toting around a bunch of cartridges.
The parts are all available from Adafruit, though you'd be able to source them from elsewhere if desired. The tricky part for most will be the shell itself, which is made using 3D printing -- not easily done if you haven't run out to grab your own 3D printer yet.
If that requirement doesn't trip you up, hit up the project link above (check out the video below, too) for step-by-step details, including pictures and a troubleshooting guide. After you're done, check out our DIY tag portal for more projects.