WordpressUnderscore.php is a wordpress-friendly fork of the Underscore.php PHP port of Underscore.js.

__u().fn() or __u::fn() 

instead of

__().fn() or __::fn() 

See above links for details of the actual funtions.

In addition to porting Underscore's functionality, Underscore.php includes matching unit tests. Thanks to Jeremy Ashkenas and all contributors to Underscore.js.

For docs, license, tests, change log, and downloads, see: http://brianhaveri.github.com/Underscore.php

Because it's tiny and only useful for developers.

If you're a developer and unfamiliar with Composer, go check it out. You can use it to load utility libraries into your plugins or themes.