The debugger engine is used in various debuggers, such as
WinDbg
CDB
NTSD
KD
Because these debuggers use the same engine, they share the commands and don't differ in their functionality very much.
User mode
Kernel mode
GUI/Console
cdb
x
Console
ntsd
x
Console
WinDbg
x
x
GUI
kd
x
Console
Although WinDbg supports both user mode and kernel mode debugging, it only supports one at a given time.
Source path
The engine has an internal source path. It is a list of directories and source servers where the engine tries to find source files from which the currently examined target was created.
After locating a source file, the code-line that correspond to one (or more) instructions can be looked up using symbol files.
Debugger engine application
It's possible to write extensions that are based on the engine. These are referred to as debugger engine application.
The header file that declares the functions for the API is in dbgeng.h.