Tux Paint is available for Haiku, an open-source operating system inspired by BeOS, within the "Haiku Depot" software repository.
Available Tux Paint packages for various platforms (as of 2020-08-30) are listed below. (More details on Tux Paint packages in Haiku Depot may be found at depot.haiku-os.org.)
Did you know? Your school can install Tux Paint on all of its computers... today, and at no cost!