Actually they are egg warmers, not an Advent calendar, but if you put in little gifts instead of eggs you’ll get a Christmas egg warmer Advent calendar ;-)
They made me think of the knitted ‘cork warmers’ ;-)
Links:
Christmas Egg Warmer Advent Calendar (DROPS Extra 0-569) (English UK/cm)
Christmas Egg Warmer Advent Calendar (DROPS Extra 0-569) (English US/in)
German:
DROPS Extra 0-569
Here at unikatissima:
Knitted Cork Christmas Trees