OllyDbg is a 32-bit assembler level analysing debugger for Microsoft® Windows®. Emphasis on binary code analysis makes it particularly useful in cases where source is unavailable.

Special highlights are:

-- Intuitive user interface, no cryptical commands
-- Code analysis - traces registers, recognizes procedures, loops, API calls, switches, tables, constants and strings
-- Directly loads and debugs DLLs
-- Object file scanning - locates routines from object files and libraries
-- Allows for user-defined labels, comments and function descriptions
-- Understands debugging information in Borland® format
-- Saves patches between sessions, writes them back to executable file and updates fixups
-- Open architecture - many third-party plugins are available
-- No installation - no trash in registry or system directories