vbsmooth

vbsmooth, surprisingly enough, does spatial smoothing. Here's the help text:

VoxBo vbsmooth (v1.8.5/Jun 14 2011)
summary:
  smoothing-related utilities for VoxBo
usage:
  vbsmooth [flags] [<file> ...]    smooth all passed files
  vbsmooth -e <image>              estimate smoothness of image
flags:
  -vox <x> <y> <z>    specify fwhm in voxels
  -mm <x> <y> <z>     specify fwhm in mm
  -m <file>           mask file, use only for variance maps
  -r <file>           remask using mask cube or tes mask
  -s <file>           special remask (see below)
  -p <tag>            tag to prepend to outfile if not using -o
  -o <filename>       set output filename
  -h                  help
  -v                  version
notes:
  default smoothing kernel is 3x3x3 voxels

  default output filename is input filename prepended with an s

  you can override the prepend with -p

  Note that there are three remasking options.  -m divides by the mask
  (should be used for variance maps).  -r remasks using the mask
  specified.  -s remasks by smoothing the mask passed, and including
  any voxel that is more than 50 percent from within the original
  mask.