WSform is one of the most powerful form plugins I’ve ever tried since I started developing WP sites in 2010. It has features like conditional logic, E-commerce, signatures, calculations, API connections, and a lot of other powerful features (some on paid plans though). The developer is also very responsive, cares about his customers, and implemented a feature request within a couple of days! I bought the agency plan and will use WSform for all upcoming projects. Highly recommended!