Numline
A notepad that does the math.
Write, and it is answered
"120 USD to EUR", "20% of 4800", "rent = 2400" — each line resolves as you type. No equals key, no hunting for buttons.
Currencies and units
Exchange rates keep themselves current and still work offline with the last known rate. Lengths, weights, and temperatures convert in the same breath.
Names and totals
Give a number a name and reuse it anywhere. Write "total" and a group sums itself; a blank line starts the next group.
Dates too
"departure - today", "departure + 2 weeks" — countdowns and deadlines, computed in place. Notebooks stay on your device.