Web-based Helpdesks with Integration into Wordpress w/ Multisite Support

I am looking for possible options for integrating helpdesk into the WordPress dashboard.

Not a priority that the ticket data is stored in WordPress.

In a perfect world, I would like something that is based on a custom post type on the main site, and then there is an interface from the other site dashboards to submit, monitor, and reply to tickets.

I know Kayako has a plugin to integrate with WordPress, but I am not certain it will work with Multisite as I don't want the config settings available to anyone by the SuperAdmin.

Just curious if anyone knows of others such as osTicket, ZenDesk or any others that have integration options before I set off to build my own.

Thanks everyone!