The theme of today's cool *nix links is smallness. As you may be able to tell by the bias in my posts I am a major fan of small applications that can substitute for established (often enormous) programs. Fortunately, the development of such applications is still very healthy in the Linux world despite the the power of modern computers.
There are a lot of practical and small desktop applications that are pretty well known -- Sylpheed for email, gLinks(-Hacked) or Dillo for browser and so on, but there are also several small back-end applications that are less known.
Here are a couple of small applications that only a geek could love.
TinyCC [fabrice.bellard.free.fr], a *tiny* C Compiler
This thing is very cool. It compiles C 8 times faster than gcc, fast enough to allow one to use C as a scripting language -- as in "#!/usr/local/bin/tcc". It is also standards compliant, and produces optimized code ( reportedly 70% the execution time of gcc ).
KDrive Tiny X Server(s) [pps.jussieu.fr]
They were written by Keith Packard, who has recently left the XFree86 team.
There are several examples of these servers, a few of which are accelerated, unfortunately there is only documentation for two of them -- Xfbdev and Xvesa.