V8 is written in C++ and is used in Google Chrome, the open source browser from Google.
V8 implements ECMAScript as specified in ECMA-262, 5th edition, and runs on Windows (XP or newer), Mac OS X (10.5 or newer), and Linux systems that use IA-32, x64, or ARM processors.
V8 can run standalone, or can be embedded into any C++ application.
You can find more information here:
From Google Developer Day 2008 in London. Kevin Millikin discusses Google Chrome with a particular emphasis on V8, the JS engine, as well as the challenges of implementing JS, how V8 works, and the future direction of V8. (50:07)