PAW (pro-active Web filter) is a filtering HTTP proxy based on the Brazil Framework. Because the Brazil Framework and PAW are written in Java, the software is highly portable. PAW allows for easy plugin of Handlers (to filter outgoing requests) and Filters (to filter incoming data), and a GUI for end users. All the configuration files are in XML, and thus easy to modify (even without the GUI). It's aim is to provide an easy to use interface for end users and to be easily extendable by developers.
The DansGuardian Anti-Virus Scanner gives you the ability to virus-scan all content that passes through DansGuardian. It uses the scanning code from the MailScanner project to do the actual virus scanning, so it supports all the virus engines that the MailScanner project supports. The scanning is done as the file is being downloaded, so your current network apps don't have to be modified, etc. They just have to support using a proxy.
Reapoff (Regular Expression, Arbitrary Protocol, Opensource Filtering Firewall) is a regular expression enabled TCP/IP proxy. It operates on data using a pair of simple rule- based configuration files defining the tests and actions to perform on data. It can also sign SSL connections transparently (with MITM), applying a security policy to encrypted SSL sessions that would otherwise be allowed unchecked. The proxy forms the core part of an overall firewall solution designed to run from a RAM disk using Trinux.
ProxIRC aims to be a proxy through which one can connect to an IRC server while also being able to connect to other instant messaging systems. Right now, partial support is offered for Microsoft's MSN using libMSN. Any IRC client can be used. Status of connected users in the MSN is made thanks to a virtual channel created by the proxy. When a user wants to talk to a friend from MSN, they /join #friend and talk. The rest of the channels are provided by a true IRC server and directly forwarded by the proxy. Only messages outgoing from the IRC client (which may be anyone) are parsed to look for information intended for the proxy. Information not useful for the proxy is forwarded to the IRC server.