Note: MacFUSE has been discontinued.
MacFUSE is a FUSE-Compliant File System Implementation Mechanism for Mac OS X. MacFUSE implements a mechanism that makes it possible to implement a fully functional file system in a user-space program on Mac OS X (10.4 and above). It aims to be API-compliant with the FUSE (Filesystem in USErspace) mechanism that originated on Linux. Therefore, many existing FUSE file systems become readily usable on Mac OS X. The core of MacFUSE is in a dynamically loadable kernel extension.
How FUSE-compliant is MacFUSE? Well, enough so that many popular FUSE file systems can be easily compiled and work on Mac OS X--often out of the box. Examples of file systems that work have been tested (to varying degrees) include sshfs, ntfs-3g (read/write NTFS), ftpfs (read/write FTP), wdfs (WebDAV), cryptofs, encfs, bindfs, unionfs, beaglefs (yes, including the entire Beagle paraphernalia), and so on.
Updated on Aug 09 2011
Note from the Developer: "This project is no longer being maintained. We cannot currently help with any OS X 10.7 (or any large feline) related bugs or issues. The MacFuse Google group is a decent resource for finding forks/replacement projects."