This modifier allows to make arrays of meshes, with multiple offset types:
- constant offset
- offset relative to object width
- offset with scale and rotation based on another object
The number of duplicates can be computed based on a fixed count, fixed length
or length of a curve. Duplicate vertices can be automatically merged.
Nice docs and example files available in the wiki:
http://mediawiki.blender.org/index.php/BlenderDev/ArrayModifier