Afivo can write output in the Silo and the VTK unstructured format. The Silo format has some advantages:

Large files can be viewed more efficiently (important in 3D)
Ghost cells are included in the output, so that contours and surface plots don't 'break' near refinement boundaries

At the moment, only cell-centered variables are included in the output.

Different output formats

m_af_output::af_write_silo Write Silo files
m_af_output::af_write_vtk Write VTK files
m_af_output::af_write_plane Write data on a plane
m_af_output::af_write_line Write data along a line
m_af_output::af_write_tree Write the full mesh in binary format (for restarting)
m_af_output::af_read_tree Read the full mesh in binary format (for restarting)

See m_af_output for more details.

Silo output

Silo is the preferred output format. With this format, ghost cells are included so that no clear artifacts should be visible near refinement boundaries.

Some details about this format:

Only data from the AMR leaves (so the highest visible refinement levels) is included
In 2D and 3D, multiple quadtree/octree boxes is converted into rectangular regions for efficiency. These are written as so-called quadmeshes into a Silo multimesh.
In 1D, output is written in the curve format

VTK output

Write the grid as an unstructured grid in the VTK XML format. Not very efficient, especially in 3D. Does not properly handle the refinement boundaries.

Visualizing results

The Silo and VTK files can be visualized with Visit. Consult the Visit manual or one of the tutorials for more details.