HelpRealm is a free of charge / free of ads support ticket system for freelancers and small teams.

It provides you with a personal contact form which you then send to your customers (by linking on your business website, or by embedding via an iframe, ...). By using that form your customers can contact your support. Support requests can then be processed by you and your agents. Ticket replies are done either by the support contact form or by replying to the notification emails.