Having recently moved to a netbook, I realized again how important performance is for software development. I realized it even more when my Android phone became almost unusable after another software upgrade. As a kid I was a big fan of a computer demoscene where gifted coders showed to the world how to make the hardware do things unimaginable even by its creators (like a famous Commodore 64 FLI graphic mode). Now when the number of small devices connected to the Internet exceeds the number of computers and laptops wired to the global network, writing efficient software is a must: Facebook develops HipHop for PHP (written in C++), Google releases Native Development Kit for Android and makes Go the first compiled programming language available for the Google App Engine platform.
It is commonly argued that ANSI C is the "fastest programming language" that exists. No it's not. The language itself is neither slow nor fast, it's the implementations that are (compare Ruby and JRuby for example). However, it's true that software written in C can be usually compiled to the most efficient executable code (excluding pure assembly). No wonder that the most efficient pieces of software, like operating system kernels (Linux, BSD, Solaris, Windows, etc) or programming language VMs (Common Lisp, Python, PHP, Ruby, and even Java) are all written almost exclusively in C (not even C++).
Out of curiosity I started to look around for web software written in C and found a wonderful web server called G-Wan. It's very small and its performance looks really amazing as compared to other web servers - some enthusiastic reviews even call it The Future of the Internet and wonder why such a brilliant software is not popular. Well, G-Wan is not popular, because there is a problem. A big problem. And the name of the problem of G-Wan is Pierre Gauthier, its author. If you browse through the G-Wan's website and forum you can learn that he is a man with a really huge ego (he calls himself one of the best engineers available), who loves to criticize other people's work (like Poul-Henning Kamp's, the author of Varnish). But at the same time he does not want to publish his own source code nor make it open source, because he perceives other developers as inferior idiots, who would surely break it or at least bring nothing interesting to the existing code base. Moreover, evil government agents will try to introduce backdoors into his software and you are more secure when Pierre hides his code deep under his bed and tells you that you should trust him. And of course you do, don't you? And if you invest your time and money in G-Wan you don't have to worry at all about future development and maintenance, because even though the source code is closed, Pierre also gives you his word that he will not drop the software, and that he will never get hit by a bus (I'm not exaggerating, just read this post). I will not go deeper into his paranoia of his website being constantly attacked by Microsoft and NSA servers, because you already should have an idea about the way the guy thinks.
Edit: On the contrary to the information provided by its author, some security problems have actually been found in G-Wan. The affected version 2.10.6 is no longer available, and the issue was addressed by Pierre in his usual manner (one of the most funny claims is that nobody ever tried to confirm the bugs, while there is no archive of older G-Wan versions to verify it). Also, any links leading to the report are being actively removed from Wiki pages (see the comments to this post for details).
On the other pole there is a true pearl called Tiny C Compiler created by Fabrice Bellard. It's so insanely fast (it can compile the typical Linux kernel in less than 15 seconds!) that it can be used to write scripts or servlets in ANSI C (guess what is used internally by G-Wan to compile the servlets). With another open source project, libmicrohttpd, it can become a good alternative if you want to build a small, fast web server that can use ANSI C servlets (for example as an embedded router software). Libmicrohttpd is fully HTTP 1.0 and 1.1 compliant, and it offers several threading models, so you can tune your software and choose which one suites you best in your environment. If I was supposed to build a tiny embeddable web server, I would definitely choose open source libmicrohttpd + tcc + some personal coding over G-Wan.