rnnoise is a "Recurrent neural network for audio noise reduction". Its main contributor is [jmvalin] who has done a good bit of other work in this space including working on [amazon-chime] and contributing to [LPCNet]. It also shares some code with [opus] which makes sense since [jmvalin] is active with that project as well.
Code: https://github.com/xiph/rnnoise
As its name suggests, it uses a Recurrent Neural Network (RNN) with [GRU]s internally. It really has a lot of similarities with the noise suppression used by [amazon-chime] and I highly suggest reading an exellent writeup by [jmvalin] to understand RNNoise better even though they're different projects since they share so much functionality: https://www.amazon.science/blog/how-amazon-chimes-challenge-winning-noise-cancellation-works