What is the name of Google's proprietary web server software?

Google’s proprietary web server software is called Google Web Server, commonly abbreviated GWS.

GWS is the web-serving software Google uses for its own infrastructure and hosted services. Unlike Apache HTTP Server, Nginx, and Microsoft IIS, it is not distributed as a general-purpose product for the public. Because Google does not publish extensive technical documentation or source code for GWS, details about its internal design remain limited.

One visible clue is the HTTP response header sometimes returned by Google-owned websites. It may identify the server as “gws,” usually without revealing a public version number. The software is associated with Google’s heavily modified server environment and has been reported as being written in C++ and running on a customized Debian Linux platform.

A common misconception is that Google relies on a standard public web server such as Apache or Nginx for its main search infrastructure. Google does use and contributes to many open-source technologies, but GWS is the proprietary server software associated with serving much of its web infrastructure. The answer is therefore the product name, Google Web Server, rather than the name of a competing public server.