smalloc (Static memory buffer malloc) is simple malloc-like memory allocator library. It can be embedded in any existing C project, since it has no external dependencies. When given a big memory buffer, it will handle allocations from that buffer. You can also add new buffers to the allocator after it has been initialized, and smalloc will auto-merge adjacent buffers if possible. It was designed to be used in kernel-side RTLinux and RTAI modules.
smtpfilter is a filter for an SMTP session which passes the session through transparently in real time, except for the DATA command which is intercepted in order to scan the data for spam and/or viruses with the scanner of your choice. The sources are heavily commented. The default spam filtering is a hybrid approach that uses spamassassin to self-train the excellent spamprobe Bayesian filter which works on a per-site rather than per-user basis. The virus checking can use clamav or NAI, or any other command- line scanner.
smtpsend is a simple SMTP client to transmit an email message to an SMTP server. It is designed for use by programs that need a simple, flexible way to send email, or for experimenting with SMTP. In many cases, sendmail can do what this program does, but it is much more complex, harder to set up and use, and doesn't give you as much lower level control. This program is written in Perl and is based on Perl's Net::SMTP module. It makes a great starting point for writing SMTP client functions into your own Perl program.
socket_wrappers is an improved version of tcp_wrappers. The improvements include changing from K&R to ANSI C, removing unneeded compatibility libraries, separation of the public and private API, prepending tcpd_ to all private functions and data to prevent name collisions, updates to signal handlers so that the application's handlers aren't tampered with, dropping supplemental groups, and some build and man page improvements. Applications compiled with this library should be smaller, too.
This program sets up a socket, then execs a program that inherits that socket on an open file descriptor. You can set up just about any kind of socket. It is like socat, but for programs that know what a socket is. For example, you could have socketexec listen on a TCP port and when a client connects to that port, exec a server program that expects a connected socket as its standard input.
spooky-c is a C version of Bob Jenkin's spooky hash. The only advantage over Bob's original version is that it is in C, not C++,'and comes with some test and benchmark code. This is a very competitive hash function, but is somewhat unportable (64-bit little endian only). It's more portable than some of the contenders like CityHash.