Killer Apps architecture description

Some weeks ago a friend of mine showed me a website where the architecture of the most popular websites is explained and described (youtube, amazon,facebook) and it also showed some interesting statistics about them.

Does anyone know where can I find this information?

Why was VisiCalc called a killer app?

VisiCalc is famously known as “The killer app” for the Apple II. It sold over 700,000 copies in six years and up to one million copies during its existence. In formulas, VisiCalc uses the A1 notation.

What was Apple's killer app?

VisiCalc is considered to be Apple II's killer app. It sold over 700,000 copies in six years, and as many as 1 million copies over its history.

What was the so killer app for the Internet?

The development of electronic mail (email) was the first Internet killer application, driving Internet use as the light bulb drove the acceptance of electricity.

Was it High Scalability? specifically, the Real Life Architectures section?

-John