Examples of popular, commercial applications written in PHP? [closed]

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I was just curious to see if I could get together a list of some popular, commercial applications written 开发者_如何学JAVAwith the PHP language. I'm just curious what people have built using PHP and how well it seems to fit the application they've developed.

Some I know of are:

1. ModernBill
2. WHMCS
3. vBulletin

What else is out there?

EDIT: To clarify, I'm looking for resalable commercial applications you can purchase. i.e. think "I purchased a copy of Microsoft Windows" not "I used the Google search engine."

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How about Facebook? I hear that's popular these days.

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Digg.com and Wordpress would both be a pretty large players.

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Magento - an eCommerce package

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ExpressionEngine is written in PHP, pretty popular blogging engine.

Edit: Oh, and don't forget the site-tracker Mint and the RSS-reader Fever.

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Quoting from Wikipedia:

As of April 2007, over 20 million Internet domains had web services hosted on servers with PHP installed and mod_php was recorded as the most popular Apache HTTP Server module. Significant websites are written in PHP including the user-facing portion of Facebook, Wikipedia (MediaWiki), Yahoo!, MyYearbook, Digg, Joomla, WordPress, YouTube in its early stages, Drupal, Tagged and Moodle.

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Timely find I made here:

10 years of PHP Applications that changed the world

http://blog.fedecarg.com/2008/05/22/open-source-php-applications-that-changed-the-world/

Did you mean not-open-source or did you mean money-making companies?

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I really like activeCollab. It's a project management and collaboration tool.

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Good examples of commercial php software I'm aware of are (not in order): activecollab, vivvo cms, predator cms, interspire email marketer... but there are also many small scripts that sells well on codecanyion as far as I can see their sales statistics

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Not really a commercial app but Facebook is PHP based. If you are concerned about the load and ability to support many users I think that is a good example.

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Cube cart is another one.