BuiltWith is a new Web app that surfaces information about what Web servers, programming frameworks, JavaScript libraries and other technologies different websites use. Although you could find some of this by viewing a page’s source and scanning through it, BuiltWith makes it quick and easy to get a list of technologies used.

For example, here’s a partial list of what’s used on apple.com:

Server Information

Apache
Apache Usage Statistics – Websites using Apache
Apache has been the most popular web server on the Internet since April 1996.

Advertising

DoubleClick.Net
DoubleClick.Net Usage Statistics – Websites using DoubleClick.Net
DoubleClick enables agencies, marketers and publishers to work together successfully and profit from their digital marketing investments.

Analytics and Tracking

Omniture SiteCatalyst
Omniture SiteCatalyst Usage Statistics – Websites using Omniture SiteCatalyst
Omniture SiteCatalyst® provides your website with actionable, real-time intelligence regarding online strategies and marketing initiatives.

DoubleClick Floodlight
DoubleClick Floodlight Usage Statistics – Websites using DoubleClick Floodlight
Floodlight is feature of DoubleClick ads that allows advertisers to capture and report on the actions of users who visit their website after viewing or clicking on one of the advertiser’s ads.

JavaScript Libraries

Prototype
Prototype Usage Statistics – Websites using Prototype
Prototype is a javascript framework which aims to ease development of dynamic web applications.

script.aculo.us
script.aculo.us Usage Statistics – Websites using script.aculo.us
script.aculo.us provides you with easy-to-use, cross-browser user interface JavaScript libraries to make your web sites and web applications fly.

Aggregation Functionality

RSS
RSS Usage Statistics – Websites using RSS
A family of web feed formats used to publish frequently updated content such as blog entries, news headlines or podcasts.

Those wanted a more detailed look at the infrastructure behind their favorite sites might want to poke around on Todd Hoff’s High Scalability blog. Hoff talks to companies like Tumblr and Evernote about their architecture how they scale. He also tracks down information from other sources like Quora in posts like this one on Pinterest.

It looks like Hoff is using Squarespace, J2EE, YUI and Amazon S3 among other things.