Ecmascript (JavaScript) is a prototype-based, object-oriented scripting language that is dynamic, weakly typed and has first-class functions. JavaScript uses syntax like C. JavaScript names and naming conventions are like Java (unrelated language).

ECMAScript engines

Just-in-time compilation (JIT)
Carakan: Opera Software ASA (Opera)
Chakra: IE JScript engine
SpiderMonkey: Mozilla Gecko (Firefox) [JägerMonkey / TraceMonkey]
SquirrelFish: Apple Inc.'s Webkit (Nitro)
Tamarin: Adobe Flash (ActionScript)
V8: Google Chrome
JavaScriptCore: WebKit project (Safari)

Runtime interpreters
JScript: Internet Explorer (IE9) [Trident layout engine]
Rhino: Mozilla (Java Platform)