A software for identifying small-planet populations. RhoPop employs Gaussian mixture models in a hierarchical framework. RhoPop includes a density-mass grid of water-rich compositions from water mass fraction (WMF) 0-1.0 and a grid of volatile-free rocky compositions over a core mass fraction (CMF) range of 0.006-0.95. Both grids were calculated using the ExoPlex mass-radius-composition calculator (https://github.com/CaymanUnterborn/ExoPlex , Unterborn+ 2023). We use the dynesty nested sampler for parameter and evidence estimation (https://doi.org/10.5281/zenodo.8408702, Speagle, J.S., 2020, Skilling 2004, Skilling 2006, Feroz, F., Hobson, M.P. and Bridges, M., 2009, Neal, R.M., 2003, Handley, W.J., Hobson, M.P. and Lasenby, A.N., 2015a, Handley, W.J., Hobson, M.P. and Lasenby, A.N., 2015b). We have included two small-planet datasets from the literature: (1) the sample of precisely measured (mass and radius uncertainties of less thant 25% and 8%, respectively) planets around M dwarfs from Luque & Palle (2022) except those the authors identify as sub-Neptunes and (2) the sample of precisely measured planets (mass and radius uncertainties of less than 30%) around FGK stars of Adibekyan+ (2021). The dynesty package is licensed under the MIT license The MIT License (MIT) Copyright (c) 2017 - Present: Josh Speagle and contributors.Copyright (c) 2014 - 2017: Kyle Barbary and contributors. Permission is hereby granted, free of charge, to any person obtaining a copyof this software and associated documentation files (the "Software"), to dealin the Software without restriction, including without limitation the rightsto use, copy, modify, merge, publish, distribute, sublicense, and/or sellcopies of the Software, and to permit persons to whom the Software isfurnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in allcopies or substantial portions of the Software.