For desktop applications you should explore my FormExDesktop library whose forms are better suited, in a lot of cases, to desktop only apps than the native Basic4ppc form though there are a few pitfalls you might experience. FormEx forms have a TopMost property.
With the Door library on a normal Basic4ppc Form you might think you could do this, Obj1 is a Door library Object.
However it won't work as you might expect as a Basic4ppc Form only allows one Form to be displayed at a time on the desktop so showing a Form hides the currently displayed Form automatically. I assume that this is done to emulate what the user sees on the device. See the FormEx demo for multiple FormExs on the desktop.
EDIT:- I've just noticed you said "other application" in which case the Door library might work. I say might as I think that TopMost may only work within an application and not on the desktop as a whole but I am not sure!