a handy tool but may not be necessary unless you cut curves or can not use the other two saws

See saws.

Saws are edge cutting tools using hardened teeth on the edges of flat metal or a disk or a thin band. The size and material of the teeth will depend on the material to be cut and its thickness - thin material requires smaller teeth, soft material requires larger to remove the chips. Hand saws include hack saws for metal and coping, cross cut, rip and mitering saws for wood. Power saws include circular (round blade) for wood, glass, tile, and masonry, band (long thin loop) for wood and metal; jig saws and reciprocating saws. A circular saw may be hand held, mounted in a moveable head (chop saw) or mounted beneath a flat surface in a way that lets the blade be adjust up or down or angled (table saw). A band saw may be fixed upright, usually with a tiltable table or may be pivoted to permit the blade to move through the material gripped in a vise. A jig saw uses a short thin blade moving up and down at right angles to the body of the saw to cut curves in metal or wood. A reciprocating saw uses a larger to much larger blade moving in and out from the end of the tool for heavier cutting and cutting through walls, pipes, etc. 2006-01-18

Power tool used for making curved cuts in wooden board.

A reciprocating sawing machine having a narrow vertical blade set in a frame which has an oscillating motion.