Serproxy is a multi-threaded proxy program for redirecting network socket connections to/from serial ports, in cases where the remote end of the serial link doesn't have a TCP/IP stack (eg an embedded or microcontroller system). The proxy allows other hosts on the network to communicate with the system on the remote end of the serial link.
SmoothWall Express is a network firewall, designed with home and small business users in mind. It is based upon a security-hardened subset of the GNU/Linux operating system and is completely free to use, download, and distribute. SmoothWall Express offers facilities and features normally only seen in expensive commercial offerings.
squid_redirect uses a list of patterns to zap annoying ad banners from Web pages, inserting a placeholder image. It lives in a Web proxy and so requires no special browser facilities. It's readily customizable, small, fast, and easy to install. (In Debian/Ubuntu, this program is named "adzapper".)
The stunnel program is designed to work as an SSL encryption wrapper between remote client and local (inetd-startable) or remote server. It can be used to add SSL functionality to commonly used inetd daemons like POP2, POP3, and IMAP servers without any changes in the programs' code. It will negotiate an SSL connection using the OpenSSL or SSLeay libraries. It calls the underlying crypto libraries, so stunnel supports whatever cryptographic algorithms you compiled into your crypto package.
Tinyproxy is a light-weight HTTP/HTTPS proxy daemon for POSIX operating systems. Designed from the ground up to be fast and yet small, it is an ideal solution for use cases such as embedded deployments where a full featured HTTP proxy is required, but the system resources for a larger proxy are unavailable.