What kind of knife is this?
It is a multi-tool, which appear to have been given out as novelties. The bottle opener and serrated knife are obvious, the slits are there to act as a pot strainer, the semi-circle shape and flat surface allows you to hold it against the edge of a pot and pour out the liquid while keeping solid bits in. I found a few of them on Ebay, the good links (as of this answer) are:

Vintage Farmers Co-op Creamery 1967 Bread Knife  

Vintage Multi-Purpose Knife Bottle Opener Strainer Stainless Wood Handle Japan - 
Given the nature of Ebay I can't guarantee these links will be good for long

According to the inscriptions on some they were given out by a couple of different Farmer's Co-ops and a Drilling company...does yours have any writing on it?



...and here is a picture of a pot drainer (single purpose) as it would be used.