threedhst reduces WFC3 grism exposures. It is essentially a wrapper around aXe (ascl:1109.016) and produces a catalog and other useful files; extracted 1D spectra are placed in a single file, and 2D spectra are in individual files. The code produces an HTML table with thumbnails of the direct images, 1D, and 2D spectra and supports the pipeline Unicorn (ascl:2411.019), which produces data products from the 3D-HST grism survey of four CANDELS fields. threedhst has been superceded by Grizli (ascl:1905.001).