Unsweetened chocolate is nothing more than tempered chocolate liquor. Not too pleasant to taste for all but the most die-hard chocaholics, it is little more than ground cocoa bean, though the degree of grinding and processing varies from maker to maker. Most unsweetened chocolate weighs in at about 47% chocolate solids and 52% cocoa butter (which means it melts very nicely), the final 1% is usually a stabilizer like lecithin which keeps the chocolate emulsion from breaking.
Though it might not seem so, unsweetened chocolate has all sorts of uses, especially in cake and cookie batters. Baker’s is the classic American brand of unsweetened chocolate, though these days it’s easy to find unsweetened bars by manufacturers like Scharffen Berger and Callebaut in specialty shops.