GDBFrontend
GDBFrontend is an easy, flexible and extensible gui debugger
... when you enable Enhanced Collabration. Click to Draw or use Ctrl + Shift + X shortcut to draw and Ctrl + Shift + C to clear all drawings. With Enhanced Collabration all debugger clients are synchronized on source viewing. GDBFrontend is very extensible and has powerful APIs. Some examples of GDBFrontend's extensibility.