It will work on both platforms, but if you have two different computers that you need to work on at the same time, then you will need two licenses. IOW, you can build it on Windows and the file will work on a Mac that has FileMaker also.
Sorry to butt in, but to clear it up for myself as well. If i only purchase one licensce I can still share the data/program between two computers, just can't modify simutanelously?
The license will allow you to install on a desktop computer and then lets say another laptop for you to use onthe road. Then can not be used at the same time and share data.
I don't use the two database simultaneously so I could install the same license on both since the product is sold with the windows and Mac version in same package.
However I'm waiting for an answer also from commercial people just to be sure and after I'll publish here to complete the tread!
If you are using FileMaker Pro to develop solutions on Windows and Mac, then you can install FileMaker Pro 10 on both machines. However, you cannot run them simultaneously.