Immunity Debugger!

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

x64_dbg is a 32-bit and 64-bit assembler level debugger for Windows.

The IDA Pro Disassembler and debugger is a multi-processor disassembler and debugger hosted on the Windows, Linux and Mac OS X Platforms.

Binary Ninja : A Reverse Engineering Platform

WinDbg is a multipurposed debugger for Microsoft Windows, distributed on the web by Microsoft as part of the Debugging Tools for Windows. It can be used to debug user mode applications, drivers, and the operating system itself in kernel mode. It is a GUI application, but has little in common with the more well-known, but less powerful, Visual Studio Debugger.

ODA is an online disassembler for a wide range of machine architectures, including: Alpha, ARM, AVR, Intel x86, Motorola 68000, MIPS, PDP-11, PowerPC, SPARC, Z80, and more! Upload a Windows PE file, ELF, or raw binary and then view the disassembly and object file meta date such as symbols and sections.

A very powerful, versatile, and customizable Win32/Win64 user mode debugger/disassembler. PEBrowseDbg64 Interactive is not a source code debugger, but operates at the Intel x64 instruction level and therefore at the lowest level where your program executes. The debugger fully supports Microsoft .NET managed processes and seamlessly allows interop or mixed-mode debugging. It also supports debugging child processes.

A general, open source, retargetable decompiler of machine code programs

ArkDasm is a 64-bit interactive disassembler and debugger for Windows.