Follow these steps to add a calendar view for the project.task model:
- Define a calendar view:
<record id="view_project_task_calendar" model="ir.ui.view">
<field name="model">project.task</field>
<field name="arch" type="xml">
<calendar date_start="date_start" date_stop="date_end" color="project_id">
<field name="name" />
<field name="user_id" />
</calendar>
</field>
</record>
- Add menus and actions using this view. This is left as an exercise for the reader.