Apache supports a variety of features, many implemented as compiled modules which extend the core functionality. These can range from server-side programming language support to authentication schemes. Some common language interfaces support Perl, Python, Tcl, and PHP. Popular authentication modules include mod access, mod auth, mod digest, and mod auth digest, the successor to mod_digest. A sample of other features include SSL and TLS support (mod ssl), a proxy module (mod proxy), a URL rewriter (implemented under mod rewrite), custom log files (mod log config), and filtering support (mod include and mod ext filter).
Popular compression methods on Apache include the external extension module, mod gzip, implemented to help with reduction of the size of web pages served over HTTP. ModSecurity is an open source intrusion detection and prevention engine for web applications. Apache logs can be analyzed through a web browser using free scripts such as AWStats/W3Perl or Visitors.
Virtual hosting allows one Apache installation to serve many different actual websites. For example, one machine with one Apache installation could simultaneously serve www.example.com, www.test.com, test47.test-server.test.com, etc.
Apache features configurable error messages, DBMS-based authentication databases, and content negotiation. It is also supported by several graphical user interfaces.