RTL-Entropy is a Linux based entropy generator which uses the RTL-SDR as the entropy source. It works by using the RTL-SDR to sample atmospheric noise and then using that noise to create randomly generated numbers.
This is useful as computers are only capable of generating pseudo-random numbers, which may look random, but are not truly random. For cryptography and security, it is desirable to use true random numbers, as pseudo-random numbers can possibly be predicted. Combining this RTL-SDR based entropy source with other entropy sources may help improve security.