AnchorDockingDsgn
This is the package that provides a docked IDE instead of the default "separate windows" look of the Lazarus IDE.
Thus it'll look more like the RAD Studio™ as shown in the following screenshot:
To dock/undock a window, you have to enable option "Show headers".
For installation and other information click here.
From the Free Pascal wiki, page "AnchorDockingDsgn", as it stood on 2023-04-09 after a change by Serbod, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.