Kodak HC-110 is a liquid-concentrate film developer introduced around 1965 and widely used ever since, particularly in photojournalism and fine-art photography. It is recommended by Ansel Adams in his book, The Negative, and is a favorite of Zone System enthusiasts.
The official Kodak data sheet contains recommended developing times for practically all Kodak black-and-white films. A more comprehensive table of developing times, comprising films from other manufacturers, is available at www.digitaltruth.com. See also Greg Mironchuk's HC-110 tips and Stefan Heymann's German HC-110 page. HC-110 is unusually environmentally friendly for the simple reason that it uses a small amount of chemicals. Less than 6 mL of HC-110 syrup - which itself is not highly toxic - will develop a roll of film. Compare that to the quantity of chemicals needed in typical powdered developers.