Muriatic acid is a watered down version of Hydrochloric acid.
It is very strong and the vapors can be deadly and can cause whats called chemical pneumonia. (basically you drown in mucus)
That said, it can be very useful for certain things like cleaning concrete, bricks, block and certain other materials.
It will take super rusty parts down to completely clean steel, but really doesn't do much to grease other than float it to the surface.
Muriatic acid is what it is in CLR only way more watered down.
Some materials are not affected by it, like copper, brass, most plastics and glass.
Hard water deposits on glass shower doors is one I use it for, but you must take the door off and outside in open air.
It will also eat your skin if it gets on you.
You would feel it start burning almost immediately if it gets on you.
Muriatic really should not be used without a serious chemical mask like the ones made for chemical warfare.
On a carb for example it immediately and semi violently eats rust and deposits, but will also literally eat that type of porous metals. ( just slower)
My Son used it to clean up a plugged up radiator for his dirt bike, but walked away and left it soaking for too long (5 min maybe)
When he came back and took the radiator out the entire filler/cap neck was completely gone.
When I do a carb with it I don't let it soak more than about 30 seconds.
It won't eat away everything in that amount of time, but it breaks everything loose so it can easily be blown out with compressed air.
I get it at Ace Hardware, but it is available at pretty much every type of hardware store.