Afivo is a framework for simulations with adaptive mesh refinement (AMR) on quadtree (2D) and octree (3D) grids. The framework comes with a geometric multigrid solver, shared-memory (OpenMP) parallelism and it supports output in Silo and VTK file formats. Afivo can be used to efficiently simulate AMR problems with up to about 1 0 8 unknowns on desktops, workstations or single compute nodes. For larger problems, existing distributed-memory frameworks are better suited. The framework has no built-in functionality for specific physics applications, so users have to implement their own numerical methods . The included multigrid solver can be used to efficiently solve elliptic partial differential equations such as Poisson’s equation. Afivo’s design was kept simple, which in combination with the shared-memory parallelism facilitates modification and experimentation with AMR algorithms. The framework was already used to perform 3D simulations of streamer discharges, which required tens of millions of cells. Program Title: Afivo Program Files doi: http://dx.doi.org/10.17632/5y43rjdmxd.1 Licensing provisions: GPLv3 Programming language: Fortran 2011 External routines/libraries: Silo (LLNL) Nature of problem: Performing multiscale simulations, especially those requiring a fast elliptic solver. Solution method: Provide a framework for parallel simulations on adaptively refined quadtree/octree grids, including a geometric multigrid solver. Unusual features: The framework uses shared-memory parallelism (OpenMP) instead of MPI.