It also had an optional feature to cap the number of story-point cards in the sprint column based on an upper estimate of the team's story-point velocity. I.e. if the team can only do at max 10pts of cards per week, that's all you are allowed to queue up in sprint. This could be overwritten to force more cards into the sprint, but in practice it provided a nice safety guard from over flooding a sprint's delivery expectations.
As a developer, i actually wished Tracker had a tiny bit more complexity (eg i want to be able to track items past "accepted" and into "in production" and "validated with users"). But i would rather have a bit too little than JIRA!
Some projects I was on had very large Acceptance queues awaiting various stakeholders. It was a little awkward, and could have been better accommodated.
And, of course, the ability to reject a feature which had displeased or been ignored by users? Or failed to accomplish its business purpose?
Ah, but these connections are just cute ribbons, and would become repressive if enforced as policy. The story to "Sunset Feature X" needn't be linked to its original implementation, no?
This is why I like GitHub Projects. Devs can create and interact with issues and PRs in the normal fashion while project folk drag them between columns and back again all day.
I liken PivotalTracker to a Ferrari. It does one thing and it does it well while JIRA is like your 18 wheeler. It'll also get you A-B, but you can bring everything "in case" you might need it and modify it to hell and back. It can even carry your Ferrari. But getting it setup and moving is a nightmare. Even simple searching your history is an exercise in complexity.
Of course as with anything opinionated, if you wanted to do something outside of its core philosophy set, you basically couldn't. For better for worse, this really meant you were at least waist deep in agile's.
When Agile+Scrum first started becoming popular it was very well received because fundamentally it gave a better framework for business to understand how developers worked other than promising deadlines. But, it's success was its own poison well... that's a different story.
The killer feature was the UI. When the alternative was basically JIRA, Pivotal was so quick and easy to use. That front page view that let you see every task in a compact list, and easily drag things around to reprioritise was pretty revolutionary.
Now it seems kind of passé but it really was pretty excellent at the time.
It also just felt slicker than Jira; not the horrible laggy mess that Jira was for most of its history.