JIRA is an issue and project tracker for teams building great software.
JIRA sits at the center of your development team, connecting the people and the work being done. Track bugs and tasks, link issues to related source code, plan agile development, monitor activity, report on project status, and more.
We use JIRA. Pivotal does the job but feels like a scaled down version of everything JIRA offers and then some. I would say that if your project is small, Pivotal does the job but once you start getting into multiple teams, JIRA does it better.