Hari Wiguna has created a hand soldered 4x4x4 RGB LED cube that is about the size of a quarter!
Hari posted on Google Plus:
It is insanely tiny! [..] I could not believe they could drill a hole that small and plate it through.
Design files and code are on GitHub: 122-Worlds_Tiniest_LED_Cube
For more details, checkout the project page on Hackaday.io: