Gravity Forms

Gravity Forms starts from an assumption most of the category avoids: you already run a WordPress site, and the form belongs inside it rather than on somebody else's service.

That produces a plugin rather than a platform. Forms render on your own domain, entries land in your own database, and the licence is annual rather than metered, so collecting ten thousand responses costs exactly what collecting ten does. Logic and question types are where two decades have gone — conditional fields, calculations, file uploads and a save-and-continue link are core rather than optional extras. Customisation goes as far as your stylesheet does: the form renders inside your own theme and accepts custom CSS, so matching it to the page around it is a styling job rather than a product limit.

The cost is everything that assumption excludes. There is no free version, the entry licence covers a single site, and payments, signatures and the more useful connections arrive as add-ons whose availability depends on which tier you bought. You are also responsible for the site underneath it, which is a job in itself.