React, Flux, GraphQL, Hack, HHVM...? All of this and more!
ReactPHP is a project that provides event-driven, non-blocking I/O with the PHP language. This is a purely PHP project which is used to provide high performance functionality for applications written in PHP. It closely resembles Node.js and in essence they are similar tools.
So the two projects called React (in PHP and JS) are completely separate initiatives and while they have some overlapping functionalities with serverside rendering, there is nothing linking these two except for the name React.Tweet