MacFusion is an open source Mac application that allows you to work with files on servers across the internet, as if they were sitting on your computer. Macfusion presents a Volume in Finder, letting you use your favorite Mac applications to work with them. Macfusion works with SSH/SFTP and FTP servers.
More generally, Macfusion is a front-end to MacFUSE software. Macfusion provides a plugin API to enable the creation of plugins for other FUSE filesystems.