Hand-crafted bow saw
The bow saw, turning saw, or frame saw is the previous century's version of a band saw. It excels at cutting curves; the blade allows for long strokes that cut much faster and more evenly than a coping saw. Normally, you wouldn't be able to push such a long, thin blade through wood.
The blade can be turned to any angle. This means it can be used to resaw material from boards much longer than the saw is deep - simply angle the body of the saw away from the cutting plane.
The bow saw, however, tensions the blade such that it handles thick stock with ease - the saw shown made short work of 2" stock. It could probably handle thicker; I just haven't tried it yet.
This particular bow saw has largely been adapted from Hasluck's The Handyman's Book (1854) and from plans in a 1920s issue of The Woodworker.
The frame is the key to the bow saw blade's rigidity in use. The two arms or cheeks are separated by a crosspiece or stretcher. Brass pins project from the handles, through the lower arms; a saw blade can easily be slipped into the grooved pins of the untensioned saw.
The upper arms of the saws are joined by several loops of cord wrapped around them, as shown. A tensioning toggle sits between these loops, and is turned to shorten this cord and draw the upper saw arms together. This in turn draws the lower arms apart (with the stretcher as fulcrum), which tensions the blade.
Use strong but light cord: too much and the toggle becomes hard to turn. Way too much, and the saw becomes top-heavy and unbalanced. I used five loops of waxed whipping cord. I like the look, and it's plenty strong.
Be careful, also, not to over-tighten the toggle, or you'll cause the blade to fail prematurely.
Blades can be custom-made, in which case, you'll need to pin or rivet them between the brass pins. Or they can be purchased - on on-line source I like is Gramercy Tools - they offer blades, pins, handles, even completed saws.
A final note on the two handles. I prefer two different handles, though many designs use the same handle style on each end. Too confusing: most blades are meant to cut in only one direction. You can't cut with one hand on each handle, not effectively. Only one of my two handles is used to work the saw - the larger one. Use the second handle to orient the blade at the same angle as that used by the blade-and-pin at the long handle.
Two references: more about the Google SketchUp model of a bow saw shown above, with download link, to use or adapt as you see fit. And BugBear's bow saw page at http://www.geocities.com/plybench/bowsaw.html showcases some lovely bow saws, and features many useful links.