Corporate versions with security and active directory authentication. Rich text, images, spreadsheets in a paid-for version. Branded versions to include in your

Corporate versions with security and active directory authentication. Rich text, images, spreadsheets in a paid-for version. Branded versions to include in your own site. Since it generally requires at least two people who need to communicate then at least one of them is likely to be prepared to pay.It's not just an eyeballs=advert web2.0 thing.