There is very little in the way of Open Source that *competently* addresses or supports US payroll. What exists is typically limited "demo ware".
Which is probably just as well unless you plan to Open Source your system too.
Beyond the simple spreadsheet, there is a fairly broad ecosystem of specialized or support intensive business software that falls into a "no fun" category that gets ignored or dismissed by Open Source. This is what keeps MS Windows on the desktop and service providers in business.
