Attach embedded workbook in Webpage Excel Web App

Hi Experts..

I have seen this feature many times.. just curious, can I also use it in any Webpage.
If you look at the this URL.. ISFORMULA
at the bottom, an Excel File was attached by mentioned "Microsoft Excel Web App"..

Where I can directly write functions.. and clearly look like Excel 2013..

Just want to know..

* Do i need to store file in Skydrive..
* Is Microsoft Web App is another part of Office 365
* Do I need to go for Office 365, to upload it in a webpage.

or API/PHP like some dangerous word is involved here..

Have a read of this article
http://www.excelmashup.com/eiv

Examples
http://www.jkp-ads.com/Articles/embeddedexcel00.asp

ms blog aticle
http://blogs.office.com/b/microsoft-...-near-you.aspx

Thanks Andy for the guidance in right direction..

Thanks again.. for ruining my upcomming weekend by giving those link to read..
Happy Weekend to all others..