Microsoft determined to take the lead from Google and Yahoo by pouring more development resources into its Windows Live service.
One of the key tenets of Microsoft’s Windows Live strategy is to engage web developers that are used to develop using Php & Javascript scripting languages. And Microsoft’s Windows Live API offers some very generous licensing terms to developers.
An application can have up to 1 million unique users per month without having to pay Microsoft. Beyond that, Microsoft will charge 25 cents per user per year.
Source: Microsoft opens up on Web strategy at Mix ’07 | CNET News.com