What is Grayjay?
Grayjay is a cutting-edge app that serves as a video player and source aggregator. It allows you to stream and organize videos from various sources, providing a unified platform for your entertainment needs.
It’s mostly used as a YouTube frontend^. However, it is now launching as a desktop app for Linux, Mac and Windows.
No it’s not. SF license allows for noncommercial modification, and it is Source Available.
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So Proprietary
Again, no. The article you link specifically mentions problems with proprietary software that FUTO dislikes, not that Grayjay is proprietary.
The definition: https://www.merriam-webster.com/dictionary/proprietary
Grayjay’s license does not fit this definition.