Contains a few 2D-plane generics for simple calculations (it uses doubles, sometimes rounded).
Holds an angle between 0 and 360 (with a precision of 2 digits). Has an extreme number of helper methods to point at given points, get distances between other angles, and to flip the angle.
Holds two full double-precision points for X and Y. Has a number of helper methods to get distances in 2D space and midpoints, as well as some fancy operator functions.
Holds a Rotation2D object and a double for the velocity. Allows you to calculate points and angles off of others using operator functions.
Holds two coefficient values (for the slope and the y-intercept). Does most of the calculating for the Line2D. Not really intended to be used directly.
Holds two Point2D objects in an array. Has logic for intersecting lines and retrieving intersecting points.
Holding a center Point2D and a radius, has methods for intersection with other circles and points.
Read the wiki (which has links to the package) and get a bunch of class definitions! Those exist here.