Apertium is a free and open-source rule-based machine translation platform. Instead of neural models it translates with linguistic dictionaries and transfer rules written in XML formats, so output is predictable and communities can add new language pairs. It is aimed in particular at related and under-resourced languages, with stable pairs such as Spanish and Catalan, Occitan and Catalan, or English and Galician. Apertium is software you install and run yourself; online translation websites and desktop applications built on it also exist.
Apertium originated in OpenTrad, a project funded by the Spanish government, and was developed by the Transducens research group at the Universitat d'Alacant in Spain. It is released under the GNU General Public License, and several companies, such as Prompsit Language Engineering, Imaxin Software and Eleka Ingeniaritza Linguistikoa, contribute to its development. As a community project rather than a company, it has no commercial owner or foreign parent. Because the code is free software, an organisation can run it on its own servers, so text need not be sent to a third party.