1. Define a graph view using bars:

<record id="view_project_tasks_graph" model="ir.ui.view">
    <field name="model">project.task</field>
    <field name="arch" type="xml">
        <graph type="bar">
            <field name="user_id"/>
            <field name="stage_id"/>
        </graph>
    </field>
</record>

2. Define a pivot view:

<record id="view_project_tasks_pivot" model="ir.ui.view">
    <field name="model">project.task</field>
    <field name="arch" type="xml">
        <pivot>
            <field name="user_id" type="row"/>
            <field name="project_id" type="col"/>
            <field name="stage_id" type="col"/>
        </pivot>
    </field>
</record>

3. Add menus and actions using this view. This is left as an exercise for the reader.

If everything went well, you should see graphs that show how many tasks are assigned to which user and the state of those tasks.