In the past few years, we have covered a bunch of commercial themes and plugins that let you manage projects and tasks on your WordPress sites. Simple Project Manager is a free plugin you can use for project and client management. It lets you manage tasks and run reports.
For each project, you can store description, estimates, public/project notes, target & actual end dates, priority, and other info. Simple Project Manager can run project, task, and client reports.
Simple Project Manager is available as a free download. You can find out more about it here.