Lazarus comes with two supplied packages (anchordocking and easydockmgr) but neither is installed by default since the underlying docking mechanism is imperfect. However either one is usable, if you don't mind a few glitches.
New solutions are being worked on currently since a fully functional dockable IDE is an oft-repeated request, especially from newcomers used to VS, recent Delphis etc.
FreeSparta is another installation package which presently offers a docked IDE.