In Austria there is a type of plum which is called ‘Hauszwetschge’ (house plum). They are ripe in early autumn, small oval shaped, dark purple outside and green to dark yellow inside; eatable straight or cooked. Few years ago I planted a similar variety called Czar. They taste just like the one from my childhood memories but are more round shaped.
Here is a photo of the ‘Hauszwetschge’ which I bought in France last year.