nginx [engine x] is a HTTP server and mail proxy server.

The basic HTTP features:
    * Handling of static files, index files, and autoindexing; open file
      descriptor cache.
    * Accelerated reverse proxying without caching, simple load balancing
      and fault tolerance.
    * Accelerated support without caching of remote FastCGI servers,
      simple load balancing and fault tolerance.
    * Modular architecture.  Filters include gzipping, byte ranges,
      chunked responses, and SSI.  Multiple SSI inclusions within a
      single page can be processed in parallel if they are handled by
      FastCGI or proxied servers.
    * SSL and TLS SNI support.

Mail proxy server features:
    * User redirection to IMAP/POP3 backend using an external HTTP
      authentication server.
    * User authentication using an external HTTP authentication server
      and connection redirection to internal SMTP backend.
    * Authentication methods:
          o POP3: USER/PASS, APOP, AUTH LOGIN PLAIN CRAM-MD5
          o IMAP: LOGIN, AUTH LOGIN PLAIN CRAM-MD5
          o SMTP: AUTH LOGIN PLAIN CRAM-MD5
    * SSL support.
    * STARTTLS and STLS support.

Documentation on nginx can be found on the wiki:
    http://wiki.nginx.org/