Use Ruby to get Magento categories http://midgetontoes.com/blog/2014/03/01/use-web-service-to-get-magento-categories/

magento_categories.rb

require 'savon'

categories = []

def process(categories, category)
	categories << {:id => get_category_value(category, 'category_id'), 
		:name => get_category_value(category, 'name')}
	children = get_category_value(category, 'children')
	return if children.nil? or children[:item].nil?
	childrenItem = children[:item]
	childrenItem = [childrenItem] unless childrenItem.kind_of?(Array)
	childrenItem.each {|child| process(categories, child)}
end	

def get_category_value(category, key)
	items = category[:item].select {|item| item.has_key?(:key) and item[:key] == key }
	return items[0][:value] unless items.empty?
end	

client = Savon.client(wsdl: "http://magentolocal.com:8888/magento/api/soap/?wsdl")
sessionId = client.call(:login, :message => {:username=> 'demo', :apiKey=>'123456'}).body[:login_response][:login_return]
response = client.call(:call, :message => {:sessionId => sessionId, :resourcePath => 'catalog_category.tree'})
category = response.body[:call_response][:call_return]
process(categories, category)

puts categories