TeamWork Desk

https://www.teamwork.com/desk
Teamwork Desk is a very nice helpdesk ticket system, integrates with their project management tool (Teamwork Projects), and has an alternative pricing model.
They also have an API. I would love to see integration similar to the desk.com and zendesk with P9. I love P9, and would like to switch my IT helpdesk to Teamwork Desk, but am slow to as the P9 -> desk.com integration is super-helpful.