Is this the info you are looking for?
I created the sort of Matrix you are looking for to register time spend on tasks in a project. The basis is the normal grid with editable columns for the days.
The table behind the grid consists of project and task columns and day columns, monday to sunday.
Of course, this table is not good for other purposes than the registration of work hours, as the registered hours are spread over a number of columns. I use this table as a temporary table, just for registration purposes. On commit the hours are registered in another table that holds the work hours per day, task and project.
A long answer to say, no, I don't think a Matrix widget exists, but there are ways to work around that.
Cheers. Toon Verschoor
Sounds good Toon, am I right you did it by altering the entity model into separate attributes for monday, tuesday etecetera? so you denormalized it to create a matrix effect?