Isometric 3D was a common technique to feature some sort of 3D environment with a 2D display.
Sometimes, a different Parallel Projection was used, but this remains quite similar.
Yet it can actually be considered a 3D engine as it can allows to move and act in a 3 axis environment (X,Y,Z).
It completely skip the perspective element in 3D.
One of the most notable example on Amstrad CPC is Head Over Heels hit game.
Isometric was also used in games such as Syndicate (by Bullfrog) or other real time strategy games on 16bit machines.
This category is to include all Games or softwares which used isometric 3D and parallel projection display in general.