DFHack is an add-on for Dwarf Fortress (search for it here on Steam!) that enables mods and tools to significantly extend the game. The default DFHack distribution contains a wide variety of these tools, including bugfixes, interface improvements, automation agents, design blueprints, modding building blocks, and more. Third-party tools (e.g. mods downloaded from Dwarf Fortress Steam Workshop or the forums) can also seamlessly integrate with the DFHack framework and extend the game far beyond what can be done by just modding the