A flexible PHP Collection complete with custom Iterator
A standalone DateTime library originally based off of Carbon
Immutable collections, with filter, map, join, sort, slice, and other methods. Well-suited for functional programming and memory-intensive applications. Runs especially fast in PHP7.
The Immutable Object implementation pattern as a PHP component.
Minimalist and Typed Immutable Collections for PHP
Array manipulation library for PHP, called Arrayy!
Extension that adds support for method calls on primitive types in PHP