What Plugin is used on this website?

Hello, I’m adding price variations to the products on my website and would like a very easy way for customers to choose which quantity they want.

This is what I have on my website now: https://tinypic.host/image/WPFORUM1.8Pcuf

I’d like to have this:

https://tinypic.host/image/WPFORUM2.8POsM

Similar to what this website has:

https://tinypic.host/image/8Pevk

I’d like for the customers to be able to choose which quantity pack they want on the catalogue pages as they are scrolling as well as obviously on each of the product pages themselves.

Is there a plugin anyone can recommend for this?