Ask HN: What is the closest digital equivalent of duct tape?

Duct tape can be used to fix, build, or jerry-rig "almost anything." What's a tool, service, etc.. that you see consistently used for unintended, unusual or widely varying purposes?

My vote: The Lua interpreter. It's lightweight, robust and seems to be used everywhere: MMORPGs, Redis, CS projects, you name it and someone probably has (or tried to) attached Lua to it.