Currently, JIRA allows due dates to be scheduled for issues. The next obvious step is to allow due dates for releases. With those two pieces in place, a calendar view could be added, which would greatly improve the use of JIRA in project management. Specs for this feature:

• Calendar view that displays due dates for both issues and releases.
• Ability to see dates for an individual project, or groups of projects.
• Provide day, week, month, and three month views of data. Each view would have varying levels of detail based on how much room there is. As a very crude example, I've attached an image showing a three month view. The little green dots are supposed to be due dates for individual issues and the bigger red dots are due dates for releases. Putting your mouse over each item would give you a pop-up with the title of the item. A one-week view would provide quite a bit of detail about each item such as the summary for an issue, and for a release perhaps a graph of the percentage of issues closed for the release.
• Ability to embed different calendar views in the Dashboard. This can be used by a manager to get a snapshot for how development is going for the week/month, or by a developer to get an overview of what they're supposed to be working on for the day.

Justification for this feature:

Time management is a critical component of development and JIRA's current tools around time management are good at a granular level (management of time for individual issues), but crude at the meta level (ability to schedule out a release and all of it's sub-issues). A calendar view would allow JIRA to act as a single tool for project management in many respects.