The tax and benefit system is the higher-level instance in OpenFisca.
Its goal is to model the legislation of a country (or a more specific domain or jurisdiction) and all the countries in the world can have their own OpenFisca tax and benefit system.
A tax and benefit system contains simulation variables (source code) and legislation parameters (data).
All the tax and benefit system instances depend on the OpenFisca core engine.
The OpenFisca core engine is able to simulate any country’s legislation once it is (partially) represented as source code.
To instantiate and use OpenFisca requires choosing or creating a version that corresponds to your country, jurisdiction or domain of interest.
You can find a selection of existing OpenFisca models at: https://openfisca.org/en/packages/.
Note that there are both country and state level models.
Each instance of OpenFisca is managed and published as open source digital infrastructure by teams positioned within, or linked to, the countries or jurisdictions they are modelling. Each maintains their own instances and as they are able, contributes to OpenFisca Core and the wider OpenFisca ecology.