The Risograph is a machine much like a photocopier, but which functions more like a mechanical screen printing bed. The earliest models were produced in the early 1980s, with the first fully-automated version appearing in 1984. A photocopier produces its output by creating a digital scan of an original and printing the result through the same heat-set process used in laser printers. ... A Risograph, however, scans an original and creates a wax master based on the scan, printing copies from the master instead of the scan itself. Its function is often described as a mix between screen printing and photocopying, as it can only print one color at a time. Combining both digital and analog printing methods, the Risograph receives your image digitally and then makes a stencil by burning tiny pixelated holes into a fiber-based master. This master is then wrapped around a color drum that pushes the ink onto the paper, resulting in a print. This process happens one color at a time (just like silk screen printing), so the more colors your design has, the more times your paper needs to go through the machine.
For more examples see here