The technology I’ve built! The biggest part of that is the Wolfram Language. I originally started building the precursor of what’s now the Wolfram Language back in 1979—because I wanted to use it. And for more than three decades I’ve used it for many many things every day. And it’s not only been a practical tool for me to create technology, do science, and pursue all sorts of other things; it’s also been what’s defined my way of thinking about things.