I know you said FREE, but I can't resist on giving a plug for Klient
. Has excellent multi-network support, great user interface. Supports Plugins via Delphi SDK, C++ SDK, and C SDK. Also, the scripting languages it supports is VBScript, JScript, Perlscript, PHPScript, and RubyScript.
Its $24.95 for lifetime license, which includes upgrades to all future versions.