Google Calculator

Google's calculator has almost no chrome of its own — it lives inside the search box. Type an arithmetic expression, a unit conversion, or a function, and a fully interactive calculator widget materializes at the top of the results with the answer already computed. That zero-launch model is the point: the fastest calculator is the field you were already typing in. The rendered widget then offers a clickable keypad and scientific functions for follow-up work, bridging from natural-language query to a real tool. Because it parses free text, it tolerates messy input and shows its interpretation as you go, which doubles as error feedback. The trade-off is dependence on the connection and on Google's parser guessing that your string was meant as math at all.