Ninja Forms is an Integration we have made available to all ISP clients. While it is not meant to be used for donations, it is quite adept at creating forms for things like Volunteer signup.
To install, go to Integrations, then Add/Remove Integrations. It will be listed. Once the installation is completed, You will need to view the Integration (under the menu of the same name) to get the Account Name and API key so you can complete the setup inside your Ninja Forms Account.
