https://www.theregister.co.uk/2019/12/16/fuse_for_macos_why_a_popular_open_source_library_became_closed_source_and_commercially_licensed/

Interview In May this year, users of popular open source project FUSE for macOS noticed the source code for the latest update was missing. The project had become closed source and was no longer free for commercial use. But as The Reg discovered when we had a talk with its maintainer, there was a very good reason for that – and it's not a good look for the many companies that used it.

FUSE stands for File System in Userspace and lets developers create a custom filesystem without writing code for the kernel. If you have a database or a cloud storage system, for example, and you want it to appear to the operating system as just another set of files and folders, you can use FUSE.