NonEuclid. "For the creation of ruler and compass constructions in both the Poincaré Disk and the Upper Half-Plane Models of hyperbolic geometry." You probably don't know what that means. I barely do. But I do know this: NonEuclid allows us to model the variety of non-Euclidean geometry in which, through a point not on a given line, there are many lines parallel to that given line.
Spherical Easel. What NonEuclid is to hyperbolic geometry, Spherical Easel is to elliptical geometry. It allows us to model the variety of non-Euclidean in which there are no parallels.
A clean, quick Triangle Solver. For those times when you just want to know the answer.