Is it legal to develop a game that uses Microsoft Excel?

My husband created a popular games' scoreboard that uses the spreadsheet to calculate scoring. It has many possibilities including the use of avatars and sound to make it fun, and therefore marketable online. I am aware I cannot use the games' logo's or title. I have researched the Microsoft website, found freeware that simulates excel, but still don't know the legalities of the use of Excel or the like.Does anyone know the answer, or have any advise or alternative suggestions? It costs $75 to "ask and expert" and I imagine that someone familiar with developing software and/or licensing may know the answer.