EGD, aka the Entropy Gathering Daemon. It was written to provide a /dev/random replacement for GnuPG on systems that don't have one (such as IRIX and Tru64).
It works be executing various programs on the system, like vmstat and df, and then combining it into a pool which is mixed using SHA-1. It is written in Perl for portability. A client program connects to it using Unix domain sockets and runs through a simple protocol to gather entropy.
Another program, called PRNGD, is compatible with software that expects to talk to EGD. PRNGD is written in C and uses an internal PRNG which it periodically seeds with the output of various commands. Unlike EGD, PRNGD will never block because it doesn't have enough entropy (compare /dev/random and /dev/urandom for a similiar situation).
Programs/libraries supporting EGD include GnuPG and OpenSSL.