A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Nice idea, but if we assume you have 20 employees, means each day (each cell) must soo large that at min. the number of employees that are on vacation at the same time can be listed in that cell.
Theoretical possible, but that would make the whole calendar so large that it becomes unusable.
That's the reason why most people use a vertical calendar, one row for each employee.
Andreas.