The open-source software, called openCrys, is provided for the multiscale simulation of antisolvent and combined antisolvent-cooling crystallization. It simulates the macro- and micromixing scales, and the complete energy and population balance equations during crystal nucleation and growth. The model is based on the Reynolds-Averaged-Navier-Stokes equation, coupled with a three-environment presumed probability density function model, and the spatially varying population balance equation semidiscretized using a high resolution finite-volume method. openCrys is implemented in C++ object oriented programming language using the open-source CFD package OpenFOAM. The software is used to compare the performance of dual impinging jet, coaxial, and radial crystallizers. It is shown that improving the micromixing does not necessarily result in a narrower crystal size distribution when temperature effects are taken into account. The complex interplay of crystallizer kinetics and momentum, mass, and heat transfer makes the selection of the best mixer for a particular application to be nonobvious, which motivates the development and application of high-fidelity multiscale simulations for the design of antisolvent crystallizers.