Like many collectors, I have a soft spot for hexagonal and other unusually-shaped cancels. While going through a large lot of used Austrian stamps today I found around about 30 with octagonal cancels. Or perhaps I should say octagonal-numeral cancels, because each has a four-digit numeral at the bottom.
I haven't been able to learn anything about these cancels from the Internet, but I can say that they appeared in certain parts of Lower Austria (mainly Styria and Vorarlberg) in the period between the late 1940s and the early 1960s. The earliest example I own is dated 1947 and the latest 1964.
Here are probably the best strikes I found today:
(1) Feldbach

(2) Gross Gerungs:

(3) Kufstein:

(4) Three from Jennersdorf:



I find myself wondering whether these are perhaps the last odd-shaped cancels used anywhere in Europe.