Osgb_convert is a project mainly written in Ruby, it's free.
Super-simple pure Ruby OSGB-WGS84 conversion gem [has rough edges]
Some UK Ordnance Survey coordinate conversions in pure Ruby.
WGS84 lat/lons -> OSGB36 lat/lons-> OS Eastings & Northings
A tidied-into-a-module-and-gem tweak of Harry Wood's port of Chris Veness' http://www.movable-type.co.uk/scripts/latlong-convert-coords.html
Originally ported to Ruby by Harry Wood: http://www.harrywood.co.uk/blog/2010/06/29/ruby-code-for-converting-to-uk-ordnance-survey-coordinate-systems-from-wgs84/
(c) Chris Veness 2005-2010, (c) Harry Wood 2010-2011 Teeny portions (c) Matt Patterson 2011
Released under an LGPL license http://www.fsf.org/licensing/licenses/lgpl.html
Examples:
WGS84 lat/lon:
lon = -0.10322 lat = 51.52237 height = 0
wgs84_point = OsgbConvert::WGS84.new(lat, lon, height)
osgb36_point = wgs84_point.osgb36
osUKgridPoint = OsgbConvert::OSGrid.from_osgb36(osgb36_point)
osUKgridPoint = OsgbConvert::OSGrid.from_wgs84(wgs84_point) easting = osUKgridPoint.easting northing = osUKgridPoint.northing
gridrefLetters = osUKgridPoint.grid_ref(8) # 8 is also the default so osUKgridPoint.grid_ref would work just as well
puts "wgs84 lat: #{wgs84_point.lat}, wgs84 lon: #{wgs84_point.long}" puts "http://www.openstreetmap.org/?mlat=#{wgs84_point.lat}&mlon=#{wgs84_point.long}&zoom=16" puts "osgb36 lat: #{osgb36_point.lat}, osgb36 lon: #{osgb36_point.long}" puts "easting: #{osUKgridPoint.easting}, northing: #{osUKgridPoint.northing}. As a grid ref: #{osUKgridPoint.gridref}" puts "http://streetmap.co.uk/grid/#{osUKgridPoint.easting}#{osUKgridPoint.northing}_106"