Apache is the most popular http-(web)server in use. Over the time a whole community of open-source software projects developed around Apache, as the Apache Software Foundation.
The Apache HTTP Server Project is an effort to develop and maintain an open-source HTTP server for modern operating systems including UNIX and Windows NT. The goal of this project is to provide a secure, efficient and extensible server that provides HTTP services in sync with the current HTTP standards.
Apache has been the most popular web server on the Internet since April of 1996.
- Apache SSL CSR generation (btw, example from Verisign but you should check out CACert for a free alternative)