Why should this be included in the repository?
2D animation software that was used and co-developed by Studio Ghibli since Princess Mononoke. OpenToonz was updated to be suitable for production and open-sourced last year.
We already have Synfig for Solus which is great, but it isn't focused on hand-drawn animation like OpenToonz is.
Is it Open Source yes
How many users do you anticipate will use this software? Not many, it's a dying art :( but this might help!
Link to source tarball/zip file https://github.com/opentoonz/opentoonz/releases
There are additional features developed for OpenToonz that could be included, namely GTS, which is a scanning tool specialized for hand-drawn animation frames, and the Plugin Utilty for creating effects plugins such as their own.