Interesting DOS commands

subst and psubst
A utility to map a subdirectory to a drive letter.
subst subst /D (Deletes the substitute drive)
If SUBST e: c:\edrive were executed, a new drive letter e: would be created, showing the contents of c:\edrive. The opposite can be achieved via the join command.

Another related command is psubst, which is supposedly able to generate permanent map. And visualsubst is a convenient GUI program.