MacFUSE, by Google
Today Google is releasing MacFUSE, an open-source Mac port of the FUSE mechanism for Linux. Like FUSE, it enables developers to implement a fully functional file system in a user-space program. And since it aims to be API-compliant with the original FUSE (Filesystem in USErspace) for Linux, it makes many existing FUSE file systems readily usable on Mac OS X. The core of MacFUSE consists of a dynamically loadable kernel extension.