phpBB is free, open-source bulletin board software written in PHP and released under the GPL-2.0 licence. Organisations install it on their own web server and database to run discussion forums for members, customers or communities, as an alternative to forum areas on platforms such as Reddit or Facebook Groups. The software is distributed as downloadable code, so the operator decides where the server runs and who can access it.
The maintaining company, phpBB Limited, is registered in England with its registered office in Marlow, Buckinghamshire. It is a company limited by guarantee without share capital, so it has no shareholders and no foreign parent company. The United Kingdom is outside the EU and the EEA. For a European organisation, the main sovereignty question is therefore where a forum is hosted and who operates it. A self-installed phpBB keeps forum data on servers that the organisation controls.