The cyanotype is probably the easiest of the so-called alternative processes. It is also one of the oldest, dating from the researches of Sir John Herschel (a close friend of Fox Talbot) in the 1840s. It became widely used as the 'blueprint' for architectural drawings and copying, though it was also used from time-to-time by photographers. Its characteristic blue colour was not universally admired. Peter Henry Emerson famously declared that "no one but a vandal would print a landscape in ... cyanotype".
I use it in its 'classical' formulation. There is a modern version developed by Mike Ware which I have tried, but which I find has more exacting requirements. Based on the light sensitive nature of organic salts of iron, and the reaction with a ferricyanide to give the dye usually called Prussian Blue (anyone wishing for absolute accuracy in terminology should consult Ware's book of the same name). The process requires a negative the same size as the final print. Mine are printed from Photoshop on to overhead transparency material. While the Romantic would use the sun as the source of the required UV light, the scientist in me prefers the reliability and reproducibility of an ultra-violet lamp.
As well as the simple cyanotype, I am also interested in the combination of cyanotype and colour. This can be achieved by overprinting the cyanotype with a layer of coloured gum bichromate. Additionally, I use the cyanotype as the cyan layer over which 'yellow' and 'magenta' gum layers can be printed to yield an approximate 'full colour' image - as in 'Mannequins'. (See also Gum Bichromate for more details).