AmorphousDiskMark/MemoryMark

AmorphousDiskMark is a Mac storage benchmarking app from Katsura Shareware with a user interface like that of the Windows app, CrystalDiskMark. Benchmark tests provide MB/s and IOPS results for a chosen target volume with controls over queue depth, test size, iterations and test intervals, as well as data choices (random or zero-fill), while tests include sequential 128KB and 1MB read/write, and random 4KB read/write. AmorphousDiskMark 2.5.2 is a free download for OS X 10.8 and later.

AmorphousMemoryMark is a Mac memory performance tester from Katsura Shareware with an interface similar to AmorphousDiskMark’s. Tests include sequential and random reads/writes at various sizes with various memory instructions, intervals, etc. Results are given in GB/s, and the app also provides details about the installed memory. AmorphousMemoryMark 1.0.2 is a free download for OS X 10.8 and later.

GrandPerspective

GrandPerspective is a Mac app from Erwin Bonsma that graphically maps disk usage to show what’s taking up storage space, displaying larger files as larger rectangles with coloring to identify attributes. (This can be especially helpful when migrating to a new Mac that may have limited storage.) Filenames are shown at the bottom of the display as you hover over a rectangle, and you can reveal the file in the Finder, open it or delete it.

Other features include customizable coloring (by file type, modification date, folder, filename, etc.), customizable filters (to exclude certain files from the view), the ability to view package contents, Quick Look previews, navigation among folders and hard-link support to accomodate Time Machine’s backup structure.

GrandPerspective 2.4.0 is free, open-source donationware for OS X 10.9 and up, with older versions compatible back to Mac OS X 10.5. The latest release revises the user interface and “includes a fix for an issue that could cause crashes when scanning data volumes.” (For convenience, the app is also available in Apple’s Mac App Store at $1.99 but wasn’t up to date when checked.)

SoftRAID

SoftRAID (from Other World Computing Inc.) is a Mac disk formatting, partitioning, testing and management app with full RAID capabilities (RAID 0, 1, 1+0, 4 and 5) on any combination of Thunderbolt, FireWire, eSATA, SCSI, USB, SAS, and Fibre Channel hard drives and SSDs.
Features include bootable mirror volumes, bootable SoftRAID DVDs, fast rebuilding of mirror volumes, a very useful disk certification (testing) feature, SMART data monitoring, email notification of problems, SSD TRIM support (for OS X 10.7 and up), a command-line program (with help), workarounds to protect against Apple macOS kernel bugs, and much more.

SoftRAID 5.8.1 is priced at $179 for OS X 10.7 and up, with a fully-functional 30-day free trial available.
Note that SoftRAID doesn’t currently support Apple’s Core Storage volume format, for FileVault and Fusion drives, and macOS 10.13 (High Sierra)/APFS also needs special workarounds for startup volumes. See also: SoftRAID Compatibility Notes and FAQ.

The latest SoftRAID release follows an Apple bug fix:

New features in version 5.8.1:

• Removes the test to see if the user is running macOS 10.15 with SIP enabled. You can now run the SoftRAID application on macOS 10.15 with SIP enabled. The bug, in macOS 10.15, which caused SIP to be incompatible with SoftRAID, is fixed in macOS 10.15.1.

SoftRAID Lite is a personal version of the app, with RAID-0 and RAID-1 capabilities, disk health monitoring and many of the other features of the professional version, but not support for higher RAID levels (4, 5 and 1+0), email notifications nor Terminal commands. Customer support is via the Internet for SoftRAID Lite, while the professional version includes direct phone support.
SoftRAID Lite is priced at $49 with a free trial available. Direct phone support is a $99 option for the Lite version.

Full SoftRAID functionality for Apple’s new APFS file system (which was introduced in an undocumented version with macOS 10.13 and then revised and made mandatory with macOS 10.14 Mojave) is due in 2020:

SoftRAID 6.0 will be fully compatible with APFS disks and volumes. You’ll be able to create and manage APFS volumes and SoftRAID 6.0 will also offer extra functionality to allow you to further manipulate APFS volumes. At the same time you’ll still get all SoftRAID’s great existing functionality, whether you’re working with APFS or HFS formatted disks. If you are interested in finding out more about SoftRAID 6.0 beta please contact support@softraid.com.

Disk Inventory X

Disk Inventory X is a Mac app from Tjark Derlien for analyzing storage usage and displaying folders and files in color-coded treemaps to make it easier to quickly identify and manage files taking up the most space. You can choose volumes or folders to analyze then click on the treemap to see which files/folders are using blocks of space or vice versa.

Disk Inventory X 1.3 is freely downloadable, open-source donationware for macOS 10.13 and up, and Disk Inventory 1.0 is available to support Macs all the way back to Mac OS X 10.3.  The latest version adds support for macOS 10.15 Catalina.