There are single shot .50 cals.
Bolt action .50 cals
Semi-Automatic .50 Cals
It is just a cartridge and, like just about any cartridge, can be delivered via many different types of weapons.
The world is changing. I knew a Marine who had trained and fired one of those belt-fed MFers from a helicopter, and I’ve seen a movie where one of the characters sports a Dessert Eagle and swaggers around with it threatening his fellow bad guys. Now it’s in fashion, I guess. For making big holes in small people.
Gatling gun would be my favorite.
Those are .50 BMGs.
I had a scoped (Leupold 4.5–14×50 Mark 4) Barrett M82A1 Semi-Auto, but sold it a few years ago.
I also still have a .50 Beowulf, on an AR platform.