io.js vs. Volt vs. Play

io.js is a JavaScript platform built on Chrome's V8 runtime. This project began as a fork of Joyent's Node.js and is compatible with the npm ecosystem.

Volt is a ruby web framework where your ruby code runs on both the server and the client (via opal.) The DOM automatically update as the user interacts with the page. Page state can be stored in the URL, if the user hits a URL directly, the HTML will first be rendered on the server for faster load times and easier indexing by search engines.

Play Framework makes it easy to build web applications with Java & Scala. Play is based on a lightweight, stateless, web-friendly architecture. Built on Akka, Play provides predictable and minimal resource consumption (CPU, memory, threads) for highly-scalable applications.