The Apache httpd server

• is a powerful, flexible, HTTP/1.1 compliant web server
• implements the latest protocols, including HTTP/1.1 (RFC2616)
• is highly configurable and extensible with third-party modules
• can be customised by writing 'modules' using the Apache module API
• provides full source code and comes with an unrestrictive license
• runs on Windows NT/9x, Netware 5.x, OS/2, and most versions of Unix, as well as several other operating systems
• is actively being developed
• encourages user feedback through new ideas, bug reports and patches
• implements many frequently requested features, including:
  
  

  DBM databases for authentication

  allows you to easily set up password-protected pages with enormous numbers of authorized users, without bogging down the server.

  Customized responses to errors and problems

  Allows you to set up files, or even CGI scripts, which are returned by the server in response to errors and problems, e.g. setup a script to intercept 500 Server Errors and perform on-the-fly diagnostics for both users and yourself.

  Multiple DirectoryIndex directives

  Allows you to say DirectoryIndex index.html index.cgi, which instructs the server to either send back index.html or run index.cgi when a directory URL is requested, whichever it finds in the directory.

  Unlimited flexible URL rewriting and aliasing

  Apache has no fixed limit on the numbers of Aliases and Redirects which may be declared in the config files. In addition, a powerful rewriting engine can be used to solve most URL manipulation problems.

  Content negotiation

  i.e. the ability to automatically serve clients of varying sophistication and HTML level compliance, with documents which offer the best representation of information that the client is capable of accepting.

  Virtual Hosts

  A much requested feature, sometimes known as multi-homed servers. This allows the server to distinguish between requests made to different IP addresses or names (mapped to the same machine). Apache also offers dynamically configurable mass-virtual hosting.

  Configurable Reliable Piped Logs

  You can configure Apache to generate logs in the format that you want. In addition, on most Unix architectures, Apache can send log files to a pipe, allowing for log rotation, hit filtering, real-time splitting of multiple vhosts into separate logs, and asynchronous DNS resolving on the fly.