Calculator
A calculator you can type a whole sentence of maths into, plus the three sums that otherwise send me hunting for my phone: splitting a bill, working out a percentage, and comparing two shelf prices.
You can type straight into the box — brackets work, and a percentage after a + or a − is taken off the number in front of it, so 50 + 10% is 55.
Recent
Press = and the line gets kept here.