Tree Layout provides a blisteringly fast layout, primarily for tree-structured graphs, but it can also be used with any directed graph that is "close" to being tree-structured (multiple parents and cycles are allowed). Multiple options are provided to allow you to achieve the appearance and clarity you need in a limited amount of space.
Force Directed Layout uses the metaphor of forces in the physical world to create layouts with more radial symetry. Nodes are considered to have electrical charges which are mutually repulsive. Links act as "springs" which hold the connected nodes together. Gravity can be applied in any direction and electrical fields can be created to contain the graph within a certain area.
Layered Digraph Layout provides a layered layout for absolutely any directed graph. Nodes are placed in separate layers and link crossing are reduced.