http://www.datarescue.com/idabase/idadownfreeware.htm
Executive Summary: http://www.datarescue.com/idabase/ida-executive.pdf

The IDA Pro Disassembler and Debugger is an interactive, programmable, extendible, multi-processor disassembler hosted on Windows or on Linux. IDA Pro has become the de-facto standard for the analysis of hostile code, vulnerability research and COTS validation. See this executive overview for a summary of its features and uses.