FUSE for macOS allows you to extend macOS's native file handling capabilities via third-party file systems.
FUSE for macOS is a successor to MacFUSE, which has been used as a software building block by dozens of products, but is no longer being maintained.
insaneFS is a fully decentralized peer-to-peer filesystem based on top of FUSE. It provides POSIX file semantics, including mutable files and directories. It does all this while providing a unified global hierarchy.