MueLu is a flexible and scalable high-performance multigrid solver library released as part of the Trilinos software suite.  It provides a variety of multigrid algorithms for problems ranging from Poisson-like operators for elasticity, convection-diffusion, Navier-Stokes and Maxwell's equations, all the way to multigrid methods for coupled multiphysics systems.  Besides its strong focus on aggregration-based algebraic multigrid (AMG) methods, MueLu comes with specialized capabilities for (semi-)structured grids to perform semi-coarsening along grid lines while forming the coarse operator via a Galerkin product (in contrast to classical geometric multigrid methods).   MueLu is extensible and allows for the research and development of new multigrid preconditioning methods.   MueLu depends heavily on Tpetra and Kokkos for performance portability and good parallel performance..