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Native Client is an open-source research technology for running x86 native code in web applications, with the goal of maintaining the browser neutrality, OS portability, and safety that people expect from web apps.We've released this project at an early, research stage to get feedback from the security and broader open-source communities. We believe that Native Client technology will someday help web developers to create richer and more dynamic browser-based applications.
Google Code Developer Site [code.google.com]
There's a lot more detail on the blog:
At its core, our release consists of a runtime, a browser plugin, and a set of GCC-based compilation tools. Together, these components make it possible to build applications that run in a web browser but incorporate native code modules.Google Code Blog [google-code-updates.blogspot.com]