Thelia is an open-source e-commerce system (CMS and framework) for building custom online shops. It is built on Symfony and API Platform and uses MariaDB as its database. Standard APIs let it connect to ERP, PIM, CRM or logistics systems, including in headless architectures. Thelia has a module system and is installed as software on your own web server, for example by a web agency or an in-house IT team.
According to the project site, Thelia is published by the French company OpenStudio, based in Lyon, which has developed it since 2005 together with a community of contributors. The source code is on GitHub under the GNU GPL v3 licence. Because you can host Thelia yourself, customer and order data stay on your own infrastructure and you choose the hosting location, for example within the EU. No vendor cloud is required. Running servers, updates and security is then the responsibility of your own organisation or your implementation partner.