Since many workflows implement virtual screening capabilities on libraries of compounds, Icolos efficiently handles molecules in a multi-tier data structure comprised of compounds, enumerations and conformers. This is based on the RDKit Mol object, and keeps track of computed properties as the workflow progresses. This provides the basis for flexible write-out capabilities in a variety of standard formats and allows for efficient parallelization at both the step and workflow level to leverage high-performance computing resources.