As the name suggests, NPAPI was first developed for Netscape browsers, starting with Netscape Navigator 2.0, but was subsequently implemented by many other browsers.
It was designed to set aside space within the browser context for the plugin to render and then streams data to it. The plugin runs in-place within the page. This was radical at the time because older browsers had to launch an external application to handle unknown content.
Google said that only six NPAPI plug-ins were used by more than five percent of users in the last month and it is not really worth carrying on supporting them.
The plan is to phase out support over the coming year, starting with blocking webpage-instantiated plugins for Chrome in January 2014.
Google will temporarily whitelist the most popular NPAPI plugins. This does not include the built-in Flash plugin and PDF viewer because they don't use NPAPI any more.
Other software that uses the plug-in includes Silverlight, Unity, Google Earth, Java, Google Talk and Facebook Video.
Google wants to remove NPAPI support from Chrome "before the end of 2014, but the exact timing will depend on usage and user feedback".
The Chrome Web Store is phasing out NPAPI support and is no longer accepting apps and extensions containing NPAPI-based plugins.
Google said that NPAPI's 90s-era architecture has become a leading cause of hangs, crashes, security incidents, and code complexity.
NPAPI isn't supported on mobile devices either and Mozilla plans to block NPAPI plug-ins in December 2013.