MacsBug is Apple's assembly-level 680x0 and PowerPC debugger for Mac OS. It can be used to debug code running in most execution environments, from applications to drivers, and everything in between. It's often used as a bug-reporting tool by many 3rd-party developers, as well as Mac OS system software developers.
What's new in version 6.6.3
Includes better support for debugging MP tasks, and fixes some serious bugs in the memory setting commands when used in PCI I/O space. This version works with all of the machines released in the Summer of 2000, including the Power Mac G4 (uni- and multi-processor), Power Mac G4 Cube, the new iMac family (Ruby, Indigo, Sage, Graphite, and Snow), and the new iBook family (Indigo, Key Lime, and Graphite).