SoftICE is a memory debugger from NuMega. While it has many illegal applications (mainly breaking the locks on copy-protected software or time limited shareware) it is also an excellent tool for very low level debugging.


Marketing Spiel from their website:

The SoftICE Driver Suite is a suite of the core device driver tools that accelerate the development and debugging of Windows device drivers. The SoftICE Driver Suite includes all versions of SoftICE for Windows 3.1, 95, 98, Millennium, NT, and 2000.  Also in the suite are the popular driver development tools DriverWorks, VtoolsD, DriverAgent. This suite provides a full-featured solution for basic driver development and debugging. Driver developers will be able to build drivers for Windows 2000, Windows NT, Windows 95/98, and more, and use SoftICE on the target platform for full-featured, interactive debugging.