Julio M. Merino Vidal says, the Apache HTTP Server is the most popular web server due to its functionality, stability, and maturity. However, this does not make it suitable for all uses: slow machines and embedded systems may have serious problems running it because of its size. Here is where lightweight HTTP servers come into play, as their low-memory footprints deliver decent results without having to swap data back to disk. Similarly, these small HTTP servers are suitable to serve static content efficiently so as to allow Apache, mod_perl, mod_python, or even servlet containers to handle dynamic requests without tying up memory-hungry children to serve small images. In other words, these applications can serve as a complement to your existing full-featured web server, not as a replacement. One of these servers is thttpd, a simple, small, portable, fast, and secure HTTP server. Among its features are support for the HTTP/1.1 standard, CGIs, virtual hosts, and IPv6. Read more.