Google Chrome
The Javascript virtual machine was considered a sufficiently important project to be split off (like Adobe/Mozilla's Tamarin) and handled by a dedicated team in Denmark. Existing implementations were designed "for small programs, where the performance and interactivity of the system weren't that important" but web applications like Gmail "are using the web browser to the fullest when it comes to DOM manipulations and Javascript". The resulting V8 JavaScript engine was designed for speed and introduces new features with that in mind such as hidden class transitions, dynamic code generation, and precise garbage collection. Tests by Google show that V8 is about twice as fast as Firefox 3 and the Safari 4 beta.