ATGroups is used in SynWrite+CudaText editors as app skeleton. It contains 6 page-controls, each based on ATTabs, and maniupulates these pages: depending on Mode prop, it makes visible one, two, three etc pages, with splitters between them, so you can resize pages. Also 2x2 and 3x2 grid modes exist (some splitters are sync'ed). Allows to drag-drop tabs between all pages. Tested with TMemo as editor control, of course can be used with other memos or frames.
Group 1 cannot be empty (on closing last tab new tab is opened), other groups can be empty (on closing last focused tab group 1 gets focus).
Screenshots taken from Delphi with themed tabs (SpTBX used)
Mode 2x2 (4 groups grid)
Mode 3x2 (6 groups grid)
License: MPL 2.0 or LGPL.
Repo is the same as ATTabs: https://github.com/Alexey-T/ATTabs
Lazarus: 1.6+. Tested on: Windows, Linux gtk2, macOS.