The synocli-disk package provides some disk related tools to advanced Linux users:

• e2fsprogs
  Ext2/3/4 filesystem userspace utilities. [GPL]

• fuse
  The reference implementation of the Linux FUSE (Filesystem in Userspace) interface. [GPLv2, LGPLv2.1 (libfuse.so, libulockmgr.so)]

• TestDisk
  TestDisk is powerful free data recovery software. [GPLv2+]

• ncdu
  Ncdu is a disk usage analyzer with an ncurses interface. It is designed to find space hogs on a remote server where you don't have an entire graphical setup available, but it is a useful tool even on regular desktop systems. [MIT]

• davfs2
  Mount a WebDAV resource as a regular file system. [GPLv3]

  Before you can mount webdav folders with davfs2, you have to execute once the following commands see issue #4466:

  Create links in /usr/sbin

  sudo ln -s /usr/local/bin/mount.davfs /usr/sbin/mount.davfs
  sudo ln -s /usr/local/bin/umount.davfs /usr/sbin/umount.davfs
  

  Create the user davfs2:davfs2:

  sudo synouser --add davfs2 "" "" 0 "" 0
  sudo synogroup --add davfs2 davfs2
  

• lsscsi
  The lsscsi command lists information about SCSI devices in Linux. [GPLv2]

• dar
  DAR is a shell command that backs up from a single file to a whole filesystems, taking care of hard links, Extended Attributes, sparse files, MacOS's file forks, any inode type (including Solaris Door inodes), etc. Notes about the internals can be found here. [GPLv3]

• ddrescue
  GNU ddrescue is a data recovery tool. It copies data from one file or block device (hard disc, cdrom, etc) to another, trying hard to rescue data in case of read errors. [GNU GPL]

• duf
  Disk Usage/Free Utility - a better 'df' alternative. [MIT]

• gdu
  Fast disk usage analyzer with console interface written in Go. [MIT]

• dua
  A tool to conveniently learn about the disk usage of directories, fast! [MIT]

• dutree
  A tool to analyze file system usage written in Rust. [GPLv3]

• tdu
  Top Disk Usage. You want to know what is using all your disk space? This command-line tool estimates the disk space occupied by all files in a given path. It displays a sorted list of the biggest items. The estimation method is similar to the 'du -skx' command from GNU Coreutils package. [GPLv2]

• s3backer
  s3backer is a FUSE/NBD single file backing store via Amazon S3. You can find a demo on how to use s3backer on s3backer wiki. [GPLv2]