OpenToonz
An open-source full-featured 2D animation creation software
...The project is especially notable because it connects professional animation heritage with an open-source development model. Artists can use it for traditional frame-by-frame animation, digital production pipelines, and experimental visual workflows. It supports desktop use across major operating systems and continues to be maintained by a public contributor community. OpenToonz is best suited for animators, studios, students, and independent creators who need a powerful 2D animation tool without a proprietary license barrier.