Version 2 of my maxwell(8) rng is now at:
https://github.com/sandy-harris/maxwell
It is a fairly simple program to gather entropy from timer
fluctuations & feed results into the Linux random(4) device. Small
--only 600 lines so reasonably easy to audit -- cheap & effective.
It has not changed much since the original (2012) release. The main
changes now are a new interface (cleaner command-line option set) and
a variety of cleanups to both code & documentation.