Lex and YACC are two programs which have been used for over a decade to parse and help compile programming languages and configuration files. Even though there are books available that tell you how to use them, little or no online HOWTO-style documentation is available. This document gets you up to speed quickly. It is unique in that it is possibly the only online resource that treats this subject from a non-CS perspective. No prior knowledge of tokenizers or state machines is needed. It comes with working examples and compilation instructions.
The LARTC-HOWTO describes many advanced ways of routing and shaping traffic. Using the HOWTO, you will be able to shape traffic in myriad ways, which will help you lower latency for interactive use when others are downloading or uploading. It will also teach you how to limit certain hosts/protocols' bandwidth usage. It also explains many aspects of routing using the 'ip' tool from the iproute2 suite.
PowerDNS Backend Development Kit allows a developer to code backends which can be loaded at runtime by PowerDNS, a nameserver that reads data from different backends. The stock distribution comes with MySQL and PostgreSQL and other backends. It is also possible to do failover, loadbalancing, and geodirection from a backend.
PowerMail is a redundant and distributed system for receiving mail via SMTP and storing it for users to access with POP. The way PowerMail works is quite unorthodox, and its design emphasizes speed and efficiency. Modified Maildir mailboxes allow PowerMail to employ hardlinks to save diskspace and deliver messages with thousands of recipients instantly. PowerMail can operate self-sufficiently or cooperate with a regular MTA to support mail forwarding.
Splitpipe accepts the streamed output of a program such as tar on standard input and distributes it over multiple output volumes. These volumes contain labels that guarantee integrity, verify that the entire volume is read, and that they are read in the proper order. Combined with the built-in ring buffer, this allows for the high speed backup of full filesystems to DVD or CD.
The ANSI/ISO C++ specifcation includes a standard C++ library, also known as the STL. GCC by default comes with an implementation that does not comply with this standard, but instead partly implements an older version. STLport is a freely available implementation, based on the SGI STL implementation. It is fully-compliant, supported, and very fast. It includes special debugging facilities and interesting and useful extensions to the standard.