Main plugin: Gravity Perks
Extensions: 29 extensions (Perks) for Gravity Forms (2018)… and counting
Gravity Perks by Gravity Wiz LLC provides you with extra, very handy options and functionalities for your Gravity Forms.
Like Read only fields, minimum or/and maximum amount of words, copying values from one field to another, limiting checkboxes, choices, etc. There are almost 30 useful extensions of the Gravity Forms plugin available now.