GNU xorriso creates, loads, manipulates, and writes ISO 9660 filesystem images with Rock Ridge extensions. Files can be copied in and out. The session results get written to optical media or to filesystem objects. Rather than needing external tools for ISO 9660 production and CD/DVD/BD burning, it is a static compilation of libburnia-project.org. Thus GNU xorriso depends only on fundamental operating system facilities.
Chiron FS is a FUSE based filesystem that implements replication at the filesystem level like RAID 1 does at the device level. The replicated filesystem may be of any kind you want; the only requisite is that you mount it. There is no need for special configuration files; the setup is as simple as one mount command (or one line in fstab).
romfser is userland program for listing, extracting, and partially mangling romfs images. You can provide it with an offset in an image where the file system starts. The mangling ability is expressed in file substitution, where the new file has to be equal or smaller in size compared to the file being replaced. It can extract single files into the current directory or extract the whole filesystem while preserving the directory structure.
movemetafs is a searchable filesystem metadata store for Linux that lets users tag local files (including image, video, audio, and text files) by simply moving the files to a special folder using any file manager. It also lets users find files by tags using a boolean search query. The original files (and their names) are kept intact. movemetafs doesn't have its own user interface, but it is usable with any file manager.
libburnia is a project comprised of libraries and binaries for reading, mastering, and writing optical discs. It provides libburn, a CD/DVD/BD burn library, libisofs, a manipulation library for ISO 9660 filesystems, and libisoburn, a ISO 9660 multi-session library. On top of them there is cdrskin, a cdrecord emulator, and xorriso, a all-in-one application for ISO 9660 multi-session operations which additionaly provides a limited emulation of mkisofs.