This is a day planner/calendar widget. Originally, I started developing it as I wanted a big calendar where I could see several months at a glance (up to 12 months in this version) but it evolved into something more complex with possibility to add events and to-do tasks.
In its most compact form, the widget simply displays your to-do tasks one after the other in a small bar. Expand this bar to see the list of tasks and to edit/delete them. Click on the C button to open the calendar. You can then add an event by double-clicking on a day. More options are available when right-clicking the widget.