- What is this?

An implementation of the cool date/time methods you'll find in Rails, but for Javascript

- Why?

Why not?

- Do you use it at Skello?

As of January 2017, no.

- Should I use it?

If you want to.

- But you're overriding the Number and Date prototypes, isn't that terrible?

It's not conventional in JS, but it won't break your code.