It appears as though there is Professional, Home & Student, Small
Business, and Standard. The following URL is a comparison of which
products are included in each version:
The newsgroup where you posted your question is dedicated to Microsoft
Project, a desktop scheduling application.
The number of versions of Microsoft Office (meaning Word, Excel,
PowerPoint...) is possibly determined by the country where you are attempting
to purchase. That is, Microsoft may make different versions of the software
available depending on local languages and geography.