iNotepad isn[SQ]t a widely known or established application for Mac. There[SQ]s no standard or commonly used program with that name. It[SQ]s possible :

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It[SQ]s a very niche or obscure application:

A small developer might have created a simple notepad-style app with that name, but it wouldn[SQ]t have widespread recognition.
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It[SQ]s a typo or misremembered name:

You might be thinking of a similar app with a slightly different name (like NotePad, SimpleNote, etc.).
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It[SQ]s a custom application:

Someone might have created a program for internal use or a very specific purpose and named it iNotepad.

If you encountered this name somewhere, providing more context (where you saw it, what it was used for) might help determine what it actually refers to.