Does DIY have an app to design kitchen layouts, etc. If not, I understood that IKEA had one, but can't find it.???

DIY does have their brand on one Windows based suite of design products.

Here is a link for designing your own kitchen through IKEA.
Ikea design

Some of our clients have come back to us with not so positive feedback about Ikea kitchen planner. I have never used it to be honest.

I've used the IKEA kitchen planner. It is fun but a little difficult to achieve exact measurements. Good old graph paper and pencil are better. The Ikea planner is very nice for visualizing how the kitchen will look with different faces in 3D