  The Super Tau Charm Facility (STCF) is a proposed electron-positron collider
working at $\sqrt{s}=2\sim 7$ GeV, and the peak luminosity is designed to be
above $0.5 \times 10^{35}cm^{-2}s^{-1}$. The huge amount of scientific data
brings great challenges to the offline data processing software, including the
Monte Carlo simulation, calibration, reconstruction as well as the data
analysis. To facilitate efficient offline data processing, the offline software
of Super Tau Charm Facility (OSCAR) is developed based on SNiPER, a lightweight
framework designed for HEP experiments, as well as a few state-of-art software
in the HEP community, such as podio and DD4hep.
  This paper describes the design and implementation of the core software of
the OSCAR, which provides the foundation for the development of complex
algorithms to be applied on the large data sets produced by STCF, particularly
the way to integrate the common HEP software toolkits, such as Geant4, DD4hep
and podio, into SNiPER. The software framework also provides a potential
solution for other lightweight HEP experiments as well.
