There is a program called 'OpenOffice'. You can get it for free from Downloads.com. On the search results page, there will be an Apple version and a Windows version at the top of your list, get the one that suits you. It's freeware, so it's not something illegal you're doing. It has many programs in it that are compatible with Microsoft Office, like Microsoft Word, Excel, etc.
So basically, if you open the Spreadsheet program in OpenOffice, make this and then save it as an Excel document, then you can post it and people with Microsoft Excel can read it. It has all the same features as well, it's basically free Excel. If this isn't what he's asking or what you're looking for, then disregard this message.