With Isometrically images are created on a triangular grid. You can quickly create the illusion of 3D by using different shades for sides in different orientations.

It is really easy to use. Just tap to add a point. Tap again. And again. When you tap on the starting point the shape you outlined will be drawn. An Apple Pencil works great for this on iPad, but because it snaps to the grid it also works well on iPhone or without a stylus.

I recently updated it with advanced per-layer controls and editing.