Why? It's a very useful and good-quality tool for geologysts and Earth science-related users. I've installed it in Solus following the intructions on the github page, so I think it won't be difficult to add as a package.
Is it open source? yes!
How many users do you anticipate will use this software? Well, every user that needs to do a stereographic projection... maybe not so much but we will be really happy!
Link to source tarball/zip file: https://github.com/innstereo/innstereo/archive/master.zip