Asking about features
Asking about features is the wrong question, because most of the features mentioned don't help its users reach the end goals.
Whose tool is it?
There are two major confusions:
- Individual team members confusing project management tool with personal productivity tool.
- Personal productivity tool is a personal choice, i.e. each coworker may have different choices. It's what works best for an individual.
- Personal productivity tool can't help reach the end-goals below. To reach the end-goals, the whole team must agree on some shared Project management tools that everyone will use.
- Good project management tools should improve personal productivity, but that's a side-effect, not an end-goal. On the other hand, bad project management tools that impede personal productivity will impede its own adoption.
- Managers seeing project management tool as their tool to manage people.
What are the end goals
Visibility of work - allowing everyone to know what each coworker is going to work on. If two coworkers' work is going to conflict with each other, or if one has a good suggestion to offer to another, then having this visibility will encourage the dialogue to happen.
Status of project - exposing impediments; warning about impossible-to-meet deadlines or features that are too hard to implement; to indicate a project's readiness
Change control - making sure that changes to the production system, or to the source code, or to the hardware are well-documented, and that potential conflicts are prevented from happening.
Knowledge management - make note-sharing, record-keeping and searching easy. Anyone may share anything learned from the work - it could be some Heisenbugs, some online tutorials, or someone's hunch that a few issue tickets have a common underlying cause. Casual observations must be gathered so that patterns can be mined out.
These are just a few examples of end goals. None of these are "software features" per se. They are features (characteristics) of productive teams.
But some people say the best project management tool is a whiteboard
Judging from the end-goals, I cannot refute that.