The enterprise standard for agile software development. Jira handles sprints, backlogs, complex workflows and detailed reporting at a scale the lighter tools cannot, and its tight links to the rest of Atlassian, and to developer tooling, are why large engineering organisations run on it.
The power is real and so is the weight: it is complex to configure and overkill for a small team or non-technical work. When a project is big and genuinely agile, it is built for exactly that; when it is not, one of the simpler tools will serve better.