Redmine

Redmine is a free and open-source, web-based project management and issue tracking tool. It allows users to manage multiple projects and associated subprojects. A time tracking tool allows users to track how many hours of work are logged to a specific issue or project. Each time entry of "spent time" can be categorized by activity, and further explained with comments. By filling time estimates, project managers are able to produce better-suited project management & planning as well as follow individual user's progress.