Vicomsoft Ltd
InterGate software offers web caching, stateful inspection firewall, content filtering and network management services. Anti spam module also available. [Mac OS, Windows]
http://www.vicomsoft.com/

micro_proxy
HTTP/HTTPS proxy that runs from inetd, and uses less than 1kb of diskspace. [Unix]
http://www.acme.com/software/micro_proxy/

NetProxy
Offers web caching, site filtering, firewall, activity logging and access control. [Windows]
http://www.grok.co.uk/netproxy/

602 LAN SUITE
Offers mail server, spam filtering, antivirus, web caching, access control, firewall and activity logging. [Windows]
http://www.software602.com/products/ls/

Proxy+
Offers web caching, firewall, mail server, access control and activity logging. [Windows]
http://www.proxyplus.cz/

Apple.com: RTSP/RTP Proxy
Offers client machines within a protected network access to streaming servers outside the firewall. [Mac OS]
http://developer.apple.com/quicktime/quicktimeintro/tools/

Tinyproxy
HTTP proxy with low system resource requirements. Offers http header blocking. [Unix]
http://tinyproxy.sourceforge.net/

Surfer Protection Program
HTTP proxy that enhances user privacy by deleting (or faking) eight data elements, including the Cookie field and Referrer fields, from web browser responses. [Windows]
http://www.surferprotectionprogram.com/

Tircproxy
IRC proxy, access control available via standard Unix hosts file configuration. [Linux]
http://bre.klaki.net/programs/tircproxy/

Ositis Software, Inc.
Winproxy software offers web caching, firewall, antivirus, site filtering, spam protection and activity monitoring. [Windows]
http://www.ositis.com/

Oops! proxy server
Open source web and ftp caching proxy. [Unix, Linux, FreeBSD]
http://zipper.paco.net/~igor/oops.eng/

DeleGate
Offers caching, filtering and proxy support for most common protocols. Free downloads and reference manuals. [Windows, OS/2, Unix]
http://www.delegate.org/delegate/

ezbounce
Configurable IRC proxy. Downloads and product news.
http://druglord.freelsd.org/ezbounce/

Linkbyte Software, Inc.
ComTun Pro, offers connection sharing, firewall, spam filtering and caching. [Windows]
http://www.linkbyte.com/

Netscape Proxy Server
Offers web caching, content filtering, access control and activity reporting. [Unix, Windows]
http://wp.netscape.com/proxy/v3.5/datasheet/

ftp.proxy
Offers application layer FTP service proxying to facilitate use of service through firewalls. Supports various access control options. [Unix, Linux, BSD, Windows]
http://www.ftpproxy.org

Philtron
Filtering HTTP proxy that rewrites the HTML of the web pages that pass through it; removing unwanted/hostile content from the pages and providing enhanced user anonymity. [Written in PHP, platform independent]
http://philtron.sourceforge.net/

Dante
Circuit level proxy with firewall, supports SOCKS, msproxy and http proxy. Port redirection and bandwidth usage control available through add on modules. [Unix]
http://www.inet.no/dante/

TcpIQ
Offers connection sharing, bandwidth throttling and realtime graphical and data analysis of proxied traffic. Supports HTTP, FTP and POP3 traffic. [Windows]
http://www.tcpiq.com/

JanaServer
Offers connection sharing, monitoring and user level access control. Also offers http, email, ftp and news server functionality. [Windows]
http://www.janaserver.de/en/

WWWOFFLE
Open source caching Web proxy for offline use and low-bandwidth connections. Supports ad blocking and security filtering.
http://www.gedanken.demon.co.uk/wwwoffle/

Qbik
Wingate offers connection sharing, caching, access control, usage monitoring and firewall services. Content filtering, anti-virus and VPN options available as extras. [Windows]
http://www.wingate.com/

PServer
Offers connection sharing, content filtering and activity logging. [Java]
http://mysite.verizon.net/gjcullen/PRXYdoc.htm

Aladdin Knowledge Systems
eSafe gateway based content security providing protection against malicious software and spam/url filtering. [Windows/Linux] Also offer USB smart card for token authentication and hardware dongles for software copy protection purposes.
http://www.aladdin.com/