The pluggable interfaces in MOOSE are called `Systems`. Each `System` provides a unique capability to help you craft your application. Below is a current list of each of the `Systems`: * [Actions:](ActionsSystem) Set up the problem to be solved (custom input file syntax) * [Auxiliary Kernels:](AuxKernels) Explicit calculations that form fields * [Auxiliary Variables:](AuxVariables) Allow explicit calculations using nonlinear variables. * [BCs:](BCs) Boundary conditions * Constraints: Tying degrees of freedom to each other * [Dampers:](Dampers) Keep Newton's method on the right path * [DGKernels:](DG) Discontinuous Galerkin element boundary integrals * [DiracKernels:](DiracKernels) Point sources/sinks * [Executioners:](Executioners) Control how the simulation unfolds (Transient/Steady/etc.) * [Functions:](Functions) Flexible system for creating functions of space and time * [GeomSearch:](GeomSearch) Spatial relationships between pieces of mesh (useful for contact) * [ICs:](ICs) Initial conditions * Indicators: Relative error computations used for mesh adaptivity * [InterfaceKernels:](InterfaceKernels) Interface physics across subdomains * [[Kernels]]: PDE operators representing physics * Markers: Select elements to refine or coarsen for mesh adaptivity * [[Materials]]: Compute physical coefficients needed by [[Kernels]] * ["Discrete" Materials](Materials/DiscreteMaterial): Materials that are computed explicitly. * ["Derivative Material Interface](Materials/Derivativematerialinterface): Supplying derivatives along with materials. * [[Mesh]]: Read in / create geometry * [MeshModfiers](MeshModifiers): Modify the mesh * [MultiApps:](MultiApps) Run multiple MOOSE-based solves/codes simultaneously in parallel * NodalKernels * [[Outputs]]: Output simulation results * [Oversampling](Outputs/Oversample): Visualize higher-order solutions * [Postprocessors:](Postprocessors) Scalar reductions of field data (integrals, averages, etc.) * [Preconditioners:](Preconditioners) Accelerate linear convergence * Predictors: Accelerate nonlinear convergence by using good initial guesses * Splits: Advanced preconditioning capability * TimeIntegrators: Just like it says * [TimeSteppers:](TimeSteppers) How to advance through time * [Transfers:](Transfers) Move data between MultiApps * [[UserObjects]]: Custom calculations that can feed any other system in MOOSE * [SolutionUserObject](UserObjects/SolutionUserObject): Loading data from existing solution files. * Variables: Setup the unknowns for your problem * [Controls](Controls): System for altering input parameters at runtime.