GitFS is a fuse- and git-based remote filesystem with local cache for disconnected operation. It does periodic commits and pushes/pulls to keep a local shadow file system in sync with a remote repository. The filesystem should continue to work when you are disconnected. Merging after disconnected updates from multiple locations is left to git.
dantalian is a transparent file-tagging system using hard links. Tags (which are directories) can be accessed on the file system level (with or without fuse), allowing maximum interoperability with other applications. Tagging operations are performed with scripts, and can also be hooked into other applications. dantalian is file-agnostic and can be used with any and all types of files. Tags can be organized hierarchically and can also be tagged. With (optional) fuse support, dantalian can also create virtual tags (currently limited to tag intersections (AND), but will be expanded later), which can be accessed transparently on the filesystem level.
RioFS is a userspace filesystem for Amazon S3 buckets that runs on Linux and Mac OS X. It supports versioned and non-versioned buckets in all AWS regions. RioFS is intended as a storage backend for legacy daemons that cannot talk natively to S3. It handles buckets with many thousands of keys and highly concurrent access gracefully.