is a powerful whole-system simulator with such a killer features as checkpoints and reverse execution. It is now free of charge for open source developers.
Now it should be easier to debug the kernel and drivers.
Freely available packages include an example x86 machine running a Linux target.
KolibriOS can also be run on Simics. I used kolibri.raw image, and I attach kolibrios.simics config file to put it to simics-qsp-x86-6.0.43/targets/qsp-x86/ directory.
Simics is shipped with good documentation including step-by-step installation and beginner's guides.