The GNU Autoconf Archive is a collection of more than 450 macros for GNU Autoconf. They can be re-used without imposing any restrictions on the licensing of the generated configure script. In particular, it is possible to use them in configure scripts that are meant for non-free software.
mapSoN is an anti-spam system that uses an approach which is entirely different than other systems. Instead of trying to recognize spam by the IP address of the SMTP dialog's peer or by certain patters in the mail's body, it uses the sender's email address to decide whether the e-mail is delivered to your mailbox or not: Any email that comes from a "known" address may pass, but any email that comes from an email address seen for the first time needs special confirmation before it may pass. "Special confirmation" means that mapSoN will generate an MD5 checksum of the to-be-confirmed email and store the email in a temporary spool directory. Then it sends a request for confirmation to the address from which the mail was coming. In this request, it will include the MD5 checksum and ask the recipient to reply back and to quote that MD5 hash. Once it sees that MD5 hash again, it considers that a confirmation of the original email, delivers the deferred email from the spool to your mailbox, and adds the sender's address to the database of known addresses, so that the next time he tries to contact you, his mail will pass through immediately. This heuristic catches almost any spam email, because spammers have to fake their sender addresses in order to avoid being held responsible for their abuse. Hence, their address will most likely not be in the database of known addresses, nor will they ever receive the request for confirmation email.
libvarexp is a C++ library that allows its users to detach any kind of information from the representation of that information by providing a simple-to-use but powerful text-template mechanism. It offers application developers two functions that parse "variable" expressions in text buffers and replace them with the variable's contents. Additionally, the enduser has numerous ways not only to insert variables into his template files but to modify the variables contents on the fly, do full-blown regular expression search-and-replaces, or loop over the contents of arrays of variables. These variables are not limited to "environment variables". The programmer is free to provide a callback function to libvarexp that will be used to map a variable name to its contents. Thus, the variables your application provides can reside completely internally.
librfc2822 provides application developers with a complete parser for RFC2822 addresses. Not only can you use the library to verify that RFC2822 addresses are syntactically correct, you can also have an address split up into its semantic parts, what is needed when deciding where to route an address to, etc. What is quite unique is that librfc2822 does indeed parse all address types allowed by the standard. That includes such weird things as "address groups" or addresses with whitespace and comments throw in.
mini-httpd is a minimal Web server, designed for optimal performance, high security, and as little use of system resources as possible. It does not require more than one process or system thread to handle several requests concurrently. It features: HTTP 1.1-compliant keep-alive support, virtual hosting, Apache-compatible log format, the ability to run in a chroot sandbox, and the ability to drop all super-user privileges after acquiring the listening socket. All it can do is serve static files from the hard disk; there is no support for any kind of dynamic content.
Asynchronous DNS Resolver for Haskell is a library that provides an asynchronous DNS resolver on top of GNU ADNS. Not all options are supported, but A, MX, and PTR lookups work nicely. There is also support for retrieving generic RR types, CNAMEs, and for NSEC zone walking. The library can be expected to work with fine ADNS 1.4 or later. It might also work with version ADNS 1.3, but that hasnít been tested.
Postmaster is an Internet mail transport agent (MTA) that handles incoming ESMTP network connections and delivers accepted messages to the user's mailbox by piping it into an arbitrary local mailer (such as Procmail). It is configurable beyond anything you'll ever need, handles any number of concurrent connections without forking or using OS threading, and it is pretty efficient. It currently lacks any form of queue management, but for leaf sites that don't need to do extensive mail relaying, it is a reliable and powerful solution.