Hi Alex,
There is not currently a central location for this. Here is how I have described the differences before though:
Configurable apps - at 4.x called Instant Apps - have very focused goals. From a recent blog: "The gallery includes focused apps, each with a specific purpose including viewing a map, comparing two things, getting directions, viewing a gallery, and finding something nearby."
As far as differences in Web AppBuilder and Experience Builder go, while both are app builders,
ArcGIS Experience Builder provides support for apps that adapt better to mobile devices, fully configurable layouts, 2D/3D integration, and action triggers that connect an action in one widget to an outcome in another. These capabilities are not available in Web AppBuilder. Most of the widgets in Web AppBuilder will be incrementally rebuilt in Experience Builder. However, Esri will still continue to support Web AppBuilder.
ArcGIS Dashboards is built with the purpose of quickly and easily displaying GIS Data on a single screen using compelling charts and elements. ArcGIS Experience Builder requires more design effort than Dashboards, though you can configure Dashboard-like applications.
I hope this helps,
-Peter
