Router

Vyatta OFR (Open Flexible Router) is an open-source software that is designed to transform any standard x86 hardware into a full-featured network routing & firewall solution.

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Developer: Tom McCafferty
License: GNU General Public License (GPL)
Operating System: Platform Independent

ER or SIP Express Router is a very fast and flexible SIP (RFC3621) server.

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Developer: iptel.org
License: GNU General Public License (GPL)
Operating System: gcc = 2.9x; 3.[12] recommended, flex, bison, make, sed, tr,

The Multi Router Traffic Grapher (MRTG) is a tool to monitor the traffic load on network-links.

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Developer: MRTG
License: Freeware
Operating System: linux, windows, freebsd, osx, sun

Banhammer is an ASP based program that will allow you to ban IP addressespermanently or for a certain amount of time.

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Developer: Mike L.
License: Freeware
Operating System: Windows

The AdventNet ManageEngine OpUtils is a comprehensive set of 40+ unique system and network monitoring tools.

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Developer: AdventNet
License: Freeware
Operating System: WinNT 4.x,WinXP,Windows2000,Linux