Alternative to Pivotal Tracker


#1

We currently use pivotal tracker to manage our tasks internally. But as we are now extending to remote collaborating teams and individuals, we need something more manageable. A project management tool which allows us to control access rights per user.
Pivotal tracker is simple and useful tool, the only issue I see with it is that a project member can change tasks related to other members.This becomes unmanageable if more  people are involved and try changing each other’s tasks. We need something little bit more hierarchical.
The nearest we can achieve is use beta feature - Multi project workspace of Pivotal tracker to manage all at one place. This mean for all remote teams/ individuals we need to have a separate project and we move tasks to respective team based on requests.

Are you guys aware of any tool fit for our use case? Any suggestion on Pivotal Tracker?