There are many different RepRap extruder styles, a large proportion extrude melted plastic. Another common type extrudes pastes and other thixotropic materials. Some jet out inks or waxes. Metal extrusion is also being developed. Multi colour and dye injection are under development.
However little information exists on composite material extrusion in the DIY community.
This is intended to collect such information as can be found.
Links to off site developments can be added here.