As soon as a task is opened, Flyspray starts logging changes to that task in the History. If you are a member of a group with the //View History// permission, you can view the History Tab by clicking the History heading.

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There are a wide variety of things logged to the history, including all changed fields, [[comments]] added and edited, files attached, [[notifications|notification]] list changes etc. The history keeps track of old and new fields, and the person who made the changes. Keeping track of all these things allows for comprehensive [[reports]] to be generated by Project Managers.