FaultMod is finite-element software whose main application is 3D spontaneous dynamic rupture models of earthquakes. It is designed to be very flexible. Models can include a variety of fault geometries (planar fault, curved fault, multiple faults, branched faults, rough faults, etc.), a variety of friction laws (slip weakening, time weakening, rate-and-state, thermal pressurization, etc.), and a variety of material constitutive properties (elastic, viscous, plastic, viscoplastic, etc.). Parameters can vary with position in 3D space in any desired way. FaultMod has built-in finite-element mesh generators, and supports multiple element shapes (hexahedron, tetrahedron, wedge, pyramid). Additionally, there are multiple output drivers to produce modeling outputs in various formats.