Missing 'sticky note' app

Somehow, I have lost a sticky/post-it app from my android.
It opened as a coloured box on the right of the screen where the message could be typed - then - and this is the important bit - it could be reduced to a tiny box at the top-right of the screen, which could be clicked to re-open.
I have tried those on Play Store, but they all disappear on minimising and I/you have to remember they are there. The one I lost has that constant presence, least I should forget.
I have Google Keep and OneNote for serious stuff.
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Jim the Geordie