This is on the water main for the house, just downstream of the main shutoff valve. Water is going up in the picture, as the arrow shows. Is it a strainer? A check valve? Pressure regulator? It appears to say "Parts No. 135CM2" but I couldn't find anything matching that on google. I cannot read any part of the logo so I can't search on that.
It's a pressure regulator. The screw at the top turns in (clockwise) to increase the pressure, and turns out (counterclockwise/anticlockwise) to decrease the pressure. The plug at the bottom (adjacent to the screw) can be where a pressure gauge goes for the low pressure side, but it's plugged off. The other plug towards the input is where you can loop back into the high pressure side.
Definitely a water pressure regulator. I had one of these installed when I bought my house because the water pressure in home was 100psi and I was told by a licensed plumber that plumbing supply is engineered to sustain 80psi max before things like leaks begin to develop over time.
In my area building code dictates that a thermal expansion tank must also be added to the water heater when a regulator is installed. The pressure regulator creates a closed water circuit whereas before it would have been an open water circuit regulated by whatever pressure I had delivered by my water company from their main line.
judging by the shape it's a pressure regulator, the screw at the tip of the cone section adjusts the pressure.