Shellac is a resin secreted by the female lac bug. It was one of the most popular wood finishes in the 19th century, but still has uses today. For simplicity's sake, it is so easy to use. Just brush it on, and let it soak in. It can then be sanded or rubbed with steel wool, and then subsequent coats may be applied until the desired gloss is achieved. I also use it as a sanding sealer on pithy spalted woods even though I am going to use an oil/wax finish in the end.
Shellac is getting expensive, currently going for about $45 per gallon. But you can also make your own shellac. You can buy shellac flakes in many grades and colors, the most expensive being clear or blonde. Shellac is typically mixed with denatured alcohol ($15/gal) in various strengths or "cuts". A one pound cut has, yes, one pound of shellac per gallon volume. Commercial Shellac is typically a two or three pound cut. Given that shellac flakes go for about $20/lb, it would cost me $55 per gallon to make my own two pound cut!
For the work I do, striving for an authentic Folk Art appeal, I feel Shellac is ideal. I wouldn't want to coat my pieces in plastic (polyurethane).