Formstack offers a Salesforce App that is 100% native, meaning no additional setup, connectors, or integrations are needed. This can be downloaded from the AppExchange here: https://appexchange.salesforce.com/listingDetail?listingId=a0N3000000B5GNkEAN
Formstack also offers a separate web application on formstack.com. Formstack.com and Formstack Salesforce App are separate products and separate subscriptions are required for access to their respective features.
For more on the native Salesforce App, click here.
For more on Formstack, click here.
To see these two products side by side, please click here.