Slope Calculator
Two points in, everything about the line through them out.
The formulas
m = (y₂ - y₁) / (x₂ - x₁)
Slope is rise over run. Once you have m, the intercept is b = y₁ - m·x₁, the distance comes from the Pythagorean theorem on the coordinate differences, and the midpoint is just the average of the coordinates.
Reading the slope
Positive slope rises left to right, negative falls, zero is horizontal, and a vertical line has undefined slope (the run is zero, and dividing by zero is not a number). Slope 2 means 2 units up for every unit across, an angle of about 63.4 degrees.