Jamhamster is a maker with an affinity for retro hardware, and we're right there with him! For this project, he managed to fit a Raspberry Pi Zero inside of a custom cassette tape to emulate an old ZX Spectrum computer.
The cassette features artwork boasting "ZX Spectrum" in the title box. This isn't an original cassette; the label was custom-designed just for this project. Inside is an aluminum plate that acts as a giant heatsink for the Pi Zero.
Fitting the Pi Zero inside wasn't easy as the width of the Pi and clearance between the reels and tape bottom don't match. According to Jamhamster, four GPIO pins had to be sacrificed. The final rig includes plenty of external ports though and even a safe shutdown button.
For audio, Jamhaster created a headphone socket and wired to the Pi Zero. The project also has a USB hub with two ports accessible from the top.
The best Raspberry Pi projects are the ones you can recreate. Check out the original thread shared by Jamhamster on Reddit to see how this project works in greater detail.