x64dbg is an Open Source x64/x32 debugger for Windows.

x64dbg Features:

Open-source
Intuitive and familiar, yet new user interface
C-like expression parser
Full-featured debugging of DLL and EXE files (TitanEngine)
IDA-like sidebar with jump arrows
IDA-like instruction token highlighter (highlight registers etc.)
Memory map
Symbol view
Thread view
Content-sensitive register view
Fully customizable color scheme
Dynamically recognize modules and strings
Import reconstructor integrated (Scylla)
Fast disassembler (BeaEngine)
User database (JSON) for comments, labels, bookmarks etc.
Plugin support with growing API
Extendable, debuggable scripting language for automation
Multi-datatype memory dump
Basic debug symbol (PDB) support
Dynamic stack view
Built-in assembler (XEDParse)