I would guess that it's for putting a crimp in thin sheet metal for folding a mitered corner. The flanges on the "bed" insure correct registration so the folded corners meet without overlap or gaps.
The blade is razor sharp, probably should have mentioned that. I was also thinking picture framing, but for cutting card photo borders, not the actual frame... but that was a WAG.
There's a type of anvil lopper for cutting miters that looks almost identical to that. The blade would be sharp if that is what it's for. The ones I've seen usually have angle marked on the aluminum section.
Thanks for the input, all I used it for so far was to make an octagonal hole on the middle of a folded shop rag to see how sharp it is.
Lowe brand, made in Germany