We have a full, two-way integration with Zendesk as of January 2019.
We do have long-term plans to fully integrate with other popular help desk tools such as Help Scout, Intercom, Freshdesk, etc. For now, users with other help desks can still utilize the "External Tickets" field.
You can add tickets from those help desks within the Create Story and regular Story dialogues. Adding a ticket link will automatically populate the help desk's icon and name to lessen confusion as well. Check out a screenshot of this in action here. This is a great way to link support tickets to your Stories.