Well, there is nothing obscure about Corel apps... They are not apps, they are applications, and yes they have a good amount of integration.
Some examples are that CorelDraw has adjustments and filters that can be applied directly inside CorelDraw without the need to even switch to PhotoPaint.
If you simply have two embedded bitmaps grouped together they can be interpreted as layers on PhotoPaint. Click to "edit them as a bitmap", work on PhotoPait and when saved, they are saved inside directly into the original Draw Document.
Transparency, gradient transparency, blending modes... all inside CorelDraw.
Of course, this depends on your workflow, but I do not have to use PhotoPaint even for this type of compositings that normally you would think you need Photoshop.
(The original image was here http://www.sxc.hu/browse.phtml?f=download&id=1267036 ages ago)
Corel is also a DPS with real multipage, this means that you can edit a magazine, with master pages, text flowing between pages, etc.
For big publications, I still would recommend Indesign. But for autonomous publications of let's say 48 pages, you can work fine in CorelDraw.
Additionally.
Almost any program that has linked assets, not embedded do that. Scribus, for example, can simply use the files linked. If you update them the result is also updated...
The new version of Davinci Resolve (15) has Fusion incorporated, which is a node's based compositing system. This makes Davinci not only a Video Editor, not only one of the best color gradient program for video but an awesome compositor... oh and with a great audio editor inside!
This comes even with the free version.
But if you talk about integration you could talk about integration to their own hardware...
I think integrating your software with this type of hardware is a great idea.
The paid version makes "integration" with a collaborative workflow.
Hit FilmExpress is a composite and an editing program in one... what more integration you want?
Blender awesome. 3D modeling, rendering, animation, compositing editing...