Bay of Blood (1971)
Chosen by me from a list of freeview movies.
An odd proto-slasher.
There is some sort of plot nonsense about inheritance and property development but mostly it's a string of random pointless killings (it spends a lot of time with a bunch of partying kids - who have no relevance to the story at all) right up to it's baffling out of nowhere ending.
There's a little style and a lot of gore but it's mostly just a bit dull.