Directory Opus is a popular file manager program, originally written for the Amiga

Amiga

The Amiga is a family of personal computers that was sold by Commodore in the 1980s and 1990s. The first model was launched in 1985 as a high-end home computer and became popular for its graphical, audio and multi-tasking abilities...

 computer system in the early to mid 1990s. Development on the Amiga version ceased in 1997, but an entirely re-written version of Directory Opus is still being actively developed and sold for the Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 operating system by GPSoftware.

Directory Opus was originally developed by, and is still written by, Australian Jonathan Potter.