Napchart is a site made for polyphasic sleep planning. It lets you plan out 24 hours visually in a circle, and share it with a short 6-digit link.
Napchart reached 100.000 saved charts July 2020.
Napchart was created in 2014 by Lars Karbo.
The idea was first validated in this reddit post.
The site has been constantly updated, before reaching it's current feature state in 2018.
A new, big update is awaited in 2021.