Where is this knock-off LEGO brick from?
As others have pointed out, these are Montini building blocks.


Montini building blocks were produced by Berco Lux in Tiel, The Netherlands between 1960-1969. The plastic is much softer and the colors are a little different.
In 1969 production was stopped because of the Lego patent.
Montini history and the conflict with Lego ( in Dutch)