osTicket is a widely-used open source support ticket system. It seamlessly integrates inquiries created via email, phone and web-based forms into a simple easy-to-use multi-user web interface. Manage, organize and archive all your support requests and responses in one place while providing your customers with accountability and responsiveness they deserve.
URL to osTicket: https://osticket.com/
Using their HTTP API custom web forms can be created.
Link to the API docs: https://docs.osticket.com/en/latest/Developer%20Documentation/API%20Docs.html
Change URL and API key in send.php according to your own installation.
Preview of this web form:
Multiple attachments can be added via the upload button.
The following software versions were used while creating this web form:
