Question Inside APK

Hi guys,

I have a small question, when I extract an APK (with 7-Zip you know) some APK files have in META-INF/MANIFEST.MF (in notepad):
Created-By: 1.0 (Android), but some other have Created-By: 1.0 (SingnApk) or Created-By: 1.0 (Oracle Corporation) or Created-By: 1.0 (Apple), etc...

Can you explain me what all that means please? The difference between Android, SignApk, Oracle, Apple, ... Thanks!