Apertium is a machine translation platform. It is free software and released under the terms of the GNU General Public License.
Apertium originally was meant for translation between closely related languages (eg. between a minority and a majority language), although it has recently been expanded to treat more divergent language pairs. To create a new machine translation system, one just has to develop linguistic data (dictionaries, rules) in well-specified XML formats.
Apertium currently has language data for (in stable version) Basque, Catalan, English, Esperanto, French, Galician, Occitan, Portuguese, Romanian, Spanish, Welsh; in the unstable version: Bengali, Romanian, Asturian, Italian, Icelandic, Nepali, Norwegian (Nynorsk and Bokmål), Swedish, Danish, Irish and Scottish Gaelic.
Apertium is a shallow-transfer machine translation system, which uses finite state transducers for all of its lexical transformations, and hidden Markov models for part-of-speech tagging or word category disambiguation.