Find Any File (FAF)

For macOS. Shareware (try first, pay later), $6.

Finds files by name, date, size etc. The perfect companion to Spotlight.

See the Find Any File page for more information and download.

Prefs Editor

For macOS. Free.

Lets you edit the preferences of any application. Like the 'defaults' command in Terminal.app, but easier to use.

See the Prefs Editor page for more information and download.

What's Open

For macOS. Free.

Lists open files on all volumes, for any user. Helps figuring who which apps prevent a volume from being ejected or unmounted.

See the What's Open page for more information and download.

Launch Services

For macOS. Free.

A tool to work with the Mac's registry. Lets you browse the entire UTI tree and look up apps that open a specific file extension or match a bundle ID.

See the Launch Services page for more information and download.

iBored

For macOS, Windows, Linux. Free.

The internet-enabled Block Oriented Editor is a tool to view and edit disk sectors and related files.

See the iBored page for more information and download.

iClip

For macOS. Shareware (try first, pay later), $14.99.

iClip manages clippings of text, images and files. It optionally automatically records the contents of the clipboard every time you copy something. I am the main developer of iClip.

See the iClip site for more information and download.