With the Serializer component it's possible to handle serializing data structures, including object graphs, into array structures or other formats like XML and JSON. It can also handle deserializing XML and JSON back to object graphs.
PHP version of Google's phone number handling library
Portable UTF-8 library - performance optimized (unicode) string functions for php.
Provides functionality that helps writing PHP code that has runtime-specific (PHP / HHVM) execution paths
Semantic versioning utilities with the addition of version constraints parsing and checking.