Portable Native Client is a technology that enables portable, secure execution of native applications in Chrome. This extension of the Native Client project brings the performance and low-level control of native code to modern web browsers without sacrificing the security and portability of the web.
PNaCl helps developers produce a platform-independent form of their native application and run it in the browser without any installs. Behind the scenes, Chrome translates PNaCl applications to machine code at runtime to achieve near-native performance. On other browsers, PNaCl applications can use Emscripten and pepper.js to maintain functionality with a minimal performance hit.