One more.

When we say entropy and random numbers, we generally mean completely
unpredictable.

Intel's RDRAND, ekey, presumably ID-Quantique's solution and others rely
for their entropy on quantum physics. If our understanding of quantum
physics is correct, then by constructing such and such circuits, a certain
bit flickes unpredictably between 0 and 1.

The linux kernels' u/random relies on math. According to fairly well
understood areas of math, an observer who sees the output cannot predict
future output.

Havege relies on complexity. It says that somes system can be too complex
to understand, that modern computers are such systems, and so measuring
some aspects of the system produces a stream of completely unpredictable
numbers. (It also uses testing to find out which aspects will do.)

According to your descriptions of what you want (Taiidan), the middle is
the right one for you: It's essentially 100% open source and the others
require you to trust either quantum physics or that impossible complexity
is commonly available. You may not understand either the math or the C but
both are accessible to you.

Arnt