GalSim (Rowe et al. 2015) is a modular toolkit aimed at simulating WFI images - especially to simulate weak lensing images of galaxies. It uses realistic Hawaii-4RG detector effects (read noise, nonlinearity, interpixel capacitance, charge spreading among pixels, reciprocity failure), a WFIRST-specific PSF, and throughput and filter curves from the current design reference mission.
GULLS uses a modified version of the Besançon Galactic model (Kerins et al. 2009, Robin et al. 2003), with source star densities scaled to match red clump giant number counts from OGLE observations (Nataf et al. 2012) and event rates to match those measured from red clump giants by the EROS, MACHO, and OGLE collaborations (Popowski et al. 2005, Sumi et al. 2006, Hamadache et al. 2006). Although the simulations presented in Penny et al. (2013) were done specifically for the Euclid mission, the general information in that paper is also applicable to WFIRST observations.
SNANA (Kessler et al. 2009) is a public software package for supernova analysis. It contains a simulator, a light-curve fitter, and a cosmology fitter. The software is designed with the primary goal of using type Ia SNe as distance indicators for the determination of cosmological parameters, but it can also be used to study efficiencies for analyses of SN rates, estimate contamination from non-Ia SNe, and optimize future surveys.
STIPS is an STScI tool that allows the user to input or select a sky scene and create a simulated image as captured by one of three space-based observatories. Modules exist for HST/WFC3, JWST/NIRCam, JWST/MIRI, and WFIRST/WFI, although the latter is relatively new and is limited to a single H4RG array. The user can create on-the-fly sky scenes by choosing from a number of stellar and galaxy populations or by uploading his/her own images or catalogs. The user can then select various instrument modes (location on sky, exposure time, number of coadds, filters, etc.) for the observations. This tool is not yet public, pending release by JWST, but queries should be made using the Contact link at the top of the page.
WebbPSF provides realistic point spread functions (PSFs) for use in data simulations, exposure time calculations, etc. WebbPSF is open source Python code and includes both a scripting interface and a GUI. Built at STScI, WebbPSF has been developed for JWST use but is being extended to include WFIRST as well.