
5 retro themes
- Transfer

Windows 2000
Let's start with this boring gray Windows theme. If you wish, you can almost completely recreate it in Ubuntu using the Gnome Redmond theme, a similar window manager and a set of icons. Follow the installation instructions here.

Nextstep
NeXTSTEP was a promising UNIX-like operating system, released in 1988 and formally ending its history in 1996. NeXTSTEP is best known as the ancestor of the somewhat famous Mac OS X.
NeXTSTEP has a very distinctive appearance. So characteristic that it served as the basis for the semi-port of the project, called GNUStep and created in order to bring the appearance of a long-forgotten OS on Linux.

The necessary files and additional information are here.
Beos
The nearly

Download - here
AmigaOS
AmigaOS 4, perhaps, should not be classified as “retro”, because the last update of this operating system came out only 56 days ago. However, AmigaOS is nothing more than nostalgic for most.

This is the GTK version of the “zami” AmigaOS 4 theme. Download - here
OS / 2
IBM's OS / 2 - initially developed in conjunction with Microsoft - was a very bright phenomenon. Once it was even called the operating system of the future. But she did not become one, losing the competition to Windows. OS / 2 had a good graphical interface for its time and for those who remember OS / 2 - its GTK version is lower.

Download - here
Afterword
The author really wanted to include the old-school Acorn in this list, but he did not find the corresponding GTK theme. Similarly for the classic Mac OS theme.