A site which plays recordings made in forests around the world. Very relaxing.

EmissionControl2 (EC2) is a standalone interactive real-time application for granular synthesis and sound file granulation. Make new sounds to use in synthesizers, samplers, or other fx-related stuff.

GreyNoise is a system that collects and analyzes data on Internet-wide scanners. GreyNoise collects data on benign scanners such as Shodan.io, as well as malicious actors like SSH and telnet worms.

The data is collected by a network of sensors deployed around the Internet in various datacenters, cloud providers, and regions.

Simply Noise is an online white, pink, and brown noise generator. Good for sleep, deadening noise, concentration, and stress. There are also apps in the iProduct and Android stores that do the same thing (both $0.99us).

An online noise and sound generator. Has multiple categories and dozens of different sounds, from thunder to to rain to singing bowls, the wind blowing through a canyon, surf sounds, wind sounds in different locales, different voices, and different brainwaves. You can stack up to five of them in a sequence. You can download them, too! Updated periodically, so check back once in a while. The iOS and Android apps are out, too.

FOSS software that uses an RTL-SDR radio receiver as a cryptographic entropy generator. Pulls samples of RF noise, processes them, and seeds an RNG with it. Written in C.