Try the UnixWare 2/7 one - loads of commands for displaying
   various system data structures.  Get the kernel stack
   trace for an active process (to see where it is sleeping).
   I have enhanced it to load additional (eg driver specific)
   commands from shared libraries found in a specific directory.
   That way you can write a device driver, dynamically load it
   and debug it's data strcutures....



sounds awfully like a limited version of gdb to me.