I’d like to implement a sidepanel in my Qt window. I search something like the one that is used in the Visual Studio (see below).

Important notes:
- The widgets don’t have to be moveable
- resizing should be possible
- each widget should be clearly separated from the other layout
Does anyone have an idea how I could build such a sidepanel? (Maybe there even exists a library)
Or does anyone know a project which uses Qt and some kind of sidepanel?
One option would be to use
QDockWidgets. That’s the type of thing they are intended for inside aQMainWindow.You can put toolbars, QTreeViews and QTableViews (or related) widgets inside your dock widget to simulate the screenshot you posted.
For an example usage: Dock Widgets Example.