You can write shapefiles (including the .dbf file) with Georuby (OSX supported)
"GeoRuby provides data types intended to hold data returned from PostGIS and the Spatial Extensions of MySql. The data model roughly follows the OGC Simple Features for SQL specification, although without any kind of advanced functionalities (such as geometric operators or reprojections). The library inputs and outputs EWKB, HexEWKB and EWKT. A recent version also includes input and output of GeoRSS and KML. The latest versions have added support for reading and writing ESRI shapefile"
To keep this in the GISse domain:
Advisory for Shapefiles - you should write shapefile (.shp, .dbf and .shx at the same time) editing .dbf on their own can cause issues if not very careful!