timer_entropyd feeds the /dev/random device with entropy data (random values) read from timers. It does this by measuring how much longer or shorter a sleep takes, since this fluctuates by a few microseconds every time. The time for a sleep jitters due to the fact that the frequency of the clocks of the timers change when they become colder or hotter. This program does not require any extra hardware. It produces around 500 bits per second. This program is also usable with virtualized systems.
Math-Random-Xorshift is a Perl module that contains a straightforward implementation of the Xorshift PRNG algorithm proposed by G. Marsaglia in 2003. The algorithm is extremely fast and passes the Diehard test, though it is not reliable enough statistically. This module is useful for games and similar applications.