The POWR Form Builder is a form builder supporting multiple platforms, Joomla of course being one of them.
They offer a lot of fairly standard form builder functions, including the following:
Email notifications on form submission
Multiple form elements - standard things like text inputs, dropdowns, but also more complex elements like star ratings, emojis etc. Captcha implementation for spam prevention
Automated email response - you can send different emails depending on how the user completed the form.
Form response dashboard - form responses are saved to your POWR dashboard.
Conditional logic - display or hide sections of the form dependent on answers already supplied by the user.
Multi-step forms - you can split up your form into multiple steps if you have a complex set of information you need to gather.
File upload inputs - files of up to 100MB can be uploaded with POWR
Post submission action - redirect users to a page after your form is submitted, limit submissions to one per user, one per page load, or hide the form.
Flexible positioning - position your form anywhere on the page, including making it popup when a user clicks on a custom floating button or on a side tab.
Limit submissions - it's possible to limit form submissions based on date ranges, or total number of form submissions (for example you have 100 prizes and you want to close the form after 100 submissions.
Integrations - POWR forms can integrate with a number of third party services including Google Sheets, Mailchimp, Google Drive, Salesforce etc. You can also integrate with any app the connects to Zapier.
The POWR Form Builder is available at a few different subscription levels, first of all they do offer a free version, obviously this is somewhat limited and more demonstrative of the capabilities of the extension - only 6 form elements are available, no file uploads are allowed, a maximum of 25 submissions per month are possible, and none of the advanced features like multi step forms or conditional elements are available. The starter plan has a maximum of 100 submissions per month and 5MB upload limit, they also add multi step forms at this level. The Pro plan has a maximum of 1000 submissions per month, and 25MB upload limit. They also include a Business plan that gives access to all of the extensions made by POWR.