Facebook is a pretty huge contributor to open source. The Three20 framework that they made which powered their original iPhone app was open source and used by tons of developers.

They have a ton of repos on their github https://github.com/facebook

If you go into IOS Settings and then click Facebook > About you can see all of the open source components that they use (An enormous amount). It has everything from AQGridView to Boost to Chromium (what?) to PHP (again, huh?).

Since Facebook is a big PHP shop, it could be that they have some standard libraries where they prefer to use PHP's version as the canonical implementation. Then they port these to various languages. In some licensing interpretations, this would bind them to the license of the original code.

Interesting. Could they be using code written in PHP, but converted to C++ using HipHop?

It's certainly possible to use C++ in native iOS apps. I'd forgotten about HipHop, so that makes a lot of sense.

For people who don't want to scroll through an endless stream of legal disclaimers and licences:

https://gist.github.com/3441055

Appirater AQGridView AutoHyperlinks Boost Chromium CocoaLumberjack CoreTextHyperlinkView EGODatabase EGOTableViewPullRefresh HPGrowingTextView jQuery JSONKit libphonenumber mosquitto OpenUDID PLCrashReporter protobuf QSUtilities Google Toolbox for the Mac Base64 library from PHP re2 SDWebImage UIImage+Alpha UIImage+Resize UIImage+RoundedCorner

> to PHP (again, huh?)

Were you not aware that Facebook is a PHP shop? Or are you just questioning its inclusion in the app's credits?

Definitely aware, just normally accustomed to license credits meaning "we used this in source code/binary form in our distributable app." I missed the fact that it was referring to the Base64 encoder/decoder which makes more sense.