Need Help Identifying This Please

[Franziska]

Double main halyard block.
Probably improved or improvised.
One end of halyard is attached on top of mast, runs down to the contraption then back up other again, over the sheave and down the mast.

Halves the power needed to pull the sometimes heavy main up.
Especially useful on full batten mains.

We have something along the same lines for our main.
Many cats have it.