NinjaCalc has a new calculator, a “Two Coordinate Geodesics” calculator that can help you analyse properties of two coordinates/points on the earths surface (defined by latitude/longitude).
Given two points in latitude/longitude form (both degrees and radians supported), the calculator can give you the great circle (shortest) distance between the two points, and the initial/final bearings. This calculator can also find an intermediate coordinate/point between the two coordinates, given a fractional amount (such as 0.5). All of these properties are calculated using the Haversine formula.
All these properties are shown on a interactive model of the earth in 3D (the sphere can be rotated).
This calculator can be found in the NinjaCalc web app at http://ninja-calc.mbedded.ninja/.