The new plugin is essentially a platform for developers to build interactive 3D web applications. It runs in JavaScript and is intended to succeed Google's previous effort in this arena, a service called Lively.
As with many of Google's efforts, this one comes with a measure of transparency. They'll be distributing this development platform under an open-source license, but according to one prominent tech blog, Google will be facing competition from a major player in the open-source market: Mozilla.
Mozilla, the purveyors of the popular Firefox web browser, are teaming up with a company called Khronos to develop a competing plugin that does approximately the same thing. According to online reports, the plugins will not be compatible.
Adult industry professionals should note that the plugin is still in a testing phase and isn't available for use on live sites yet. Google is posting updates about the new plugin, which is called the O3D API, on its official blog.
