Run a particular app on boot I have a phone running Android 4.0 and I wish to know if it is possible to turn this phone into a dedicated calculator? When I say dedicated I mean - once the phone is turned on, it boots directly to a calculator GUI? Whereby the user can immediately starting using the calculator, just like any stock standard Android calculator app would look like.

I do not wish it to boot to a home screen in between, but directly to the calculator itself. I am using a very simple example here, in anycase, would this be possible?
First, I'd like to point out that turning on is different than booting.  That said, I have a suggestion that will work if you are talking about turning the device on and off:

Use the Pin Screen feature of Android 5.0 (Lollipop). To do this, screen pinning must be enabled in Settings->Security. Once enabled, start Calculator (or any app) and then hit the "app switcher" button. This is done differently depending on what phone you have and tweaks you may have applied.  On my device, it's done by double-tapping the home key. When you are in app switcher view, touch the push pin icon on whatever app you want pinned. 

Once pinned, Calculator will be the only app that can be used. If you turn the device off and on again, you will be right back at Calculator.

Note that the pin will not persist across reboots, hence the caveat.