DFHack is a Dwarf Fortress memory access library, distributed with scripts and plugins implementing a wide variety of useful functions and tools.
The full documentation is available online here,
from the README.html page in the DFHack distribution, or as raw text in the
If you're an end-user, modder, or interested in contributing to DFHack -
go read those docs.
If that's unclear or you need more help, try the Bay12 forums thread or the #dfhack IRC channel on freenode.