Olivine is a .NET (and Java and Objective C to a lesser extent) inspired PHP class library that attempts to provide useful types for PHP.
PHP is an unplanned language that was developed in a more-or-less ad-hoc fashion. As a result, PHP did not gain a useful object system until PHP 5. So, even though PHP has things like classes, inheritance, data-hiding, namespaces and other goodies that you’d find in languages like C# and Java, it doesn’t really make use of them in the standard API.
Olivine attempts to fill that gap by implementing an API, inspired by the .NET framework, that wraps many of the built-in PHP functions.
For more information on Olivine, including some code samples, please visit the project page.