An advanced form builder for Umbraco. It's free and open source. Read the online documentation here: http://www.formulate.rocks/
Here are the highlights:
Note that "Formulate" will install Formulate and that "Formulate.Deploy" will add support for Umbraco Deploy (if you are using Formulate on Umbraco Cloud).
It is recommended that you install the NuGet package rather than the Umbraco ZIP file.