The circular saw was invented around the end of the 18th century as a rip-saw to convert logs into lumber in sawmills.
A circular saw, also known as “Skil saw”, is a tool for cutting many materials such as wood, masonry, plastic, or metal and may be hand-held or mounted to a machine. In woodworking, the term “circular saw” refers specifically to the hand-held type.
Circular saws can be either left or right-handed, depending on the side of the blade where the motor sits.
To keep a circular saw straight over a long distance, it would need a track. You can also clamp down a straight edge of some sort and run it along that line.
Circular saws are commonly powered by electricity, but cordless versions are also available that are powered by rechargeable batteries.