PAOS (Physical Optics Simulator) performs physical optics propagation simulations using Fourier optics and the Fresnel approximation to model the behavior of optical fields through complex optical systems. It combines paraxial ray tracing with wavefront propagation methods to analyze diffraction, wavefront aberrations, and imaging effects in user-defined optical configurations. The package accepts configurable input systems via files or interfaces, supports modeling of apertures, optical elements, and aberrations, and outputs propagated fields and related diagnostic data. PAOS includes command-line and library interfaces along with interactive notebooks for exploration and visualization of simulation results. Its modular design allows users to apply different propagation and aberration models, generate surface error fields, and retrieve metrics such as wavefront properties and optical system responses.

ExoSim 2 (Exoplanet Observation Simulator 2) makes spectro-photometric observations of transiting exoplanets from space, ground, and sub-orbital platforms. It is a complete rewrite of ExoSim (ascl:2002.008); it is implemented in Python 3 and uses object-oriented design principles. The package follows a three-step workflow: the creation of focal planes, the production of Sub-Exposure blocks, and the generation of non-destructive reads (NDRs). ExoSim 2 has demonstrated consistency in estimating photon conversion efficiency, saturation time, and signal generation. The simulator has also been validated independently for instantaneous read-out and jitter simulation, and for astronomical signal representation.