Gravity Forms is one of the original form plugins for WordPress. There is no free version of this plugin so you won’t find it on WordPress.org. That hasn’t stopped people from finding it though. More than one million WordPress sites use this form plugin. You can use Gravity Forms for contact forms, newsletter signups, payment forms, event registration, polls, quizzes and so on.
You have full control over which fields are used and in what order. Multiple forms can be created and inserted via shortcodes. There are many add-ons for the plugin. The add-ons you have access to depends on which license you purchase. The Personal license is $39 and is suitable for use on one site and does not include add-ons. The Business license is $99 and comes with about 10 add-ons, mostly for mailing list integration.
If you want to use the plugin on many websites and/or want the full selection of add-ons, the Developer license ($199) is your best choice. The Developer license includes add-ons for payment gateways, polls/quizzes, user registration, Help Scout and others. See the Gravity Forms website for complete details.
Compare Gravity Forms with free WordPress form plugins like Contact Form 7 and “Freemium” choices such as Ninja Forms (free core plugin with paid add-ons).