1. Customer reports a defect
2. Programmer figures out there are two tasks that needs to be done by different people (in different places). One task depend on the other.
3. The first task is solved. How does the other person know to start?
4. The second task is re-assigned and then solved.
Actually, it doesn't have to be this complex. But at least have that in mind when showing your product; all todo-applications can tackle the easy stuff, it's when the more complex use-cases appear that most of them fall apart.
And when you say "make it possible for everyone to participate" I hear "no way to figure out what you need to do". Although it's good to have a place to see everything, I'm more often interested in only what I need to participate in. Show us that please!
Even though I'm familiar with pivotal/ticketing systems, I still wanted to be sold on what it does not just on how it does it.