Corel Linux first launched in 1999, from the same company that at the time owned the WordPerfect word processing software. While it was made to compete with Microsoft's Windows it quickly died off.
Tabbing is a nice feature that allows you to tab windows together. This can be combined with the “autogrouping” feature that is provided via the apps-file. This will make certain applications tab together by default.
Tabs can eiher be embedded into the window’s titlebar as shown in the upper screenshot or they can appear as little tabs at the outside of a window such as the lower example. The position and size of the outside-tabs is customizable.
Yep, that’s Fluxbox tabs.
https://web.archive.org/web/20240202172611/http://fluxbox.org/features/