The reference documentation is [the Nimbus Book](https://nimbus.guide): it explains all the ways in which you can play with Nimbus, and use Nimbus to either monitor the eth2 chain or become a fully-fledged validator.
The latest Eth2 testnet, [Prater](https://twitter.com/Butta_eth/status/1374383003011452937), is now open to the public.
Prater's objective is to ensure that the network remains stable under a higher load than we've seen so far on mainnet -- the genesis count for Prater was 210k (almost double the size of the Beacon Chain Mainnet).
For more, see the [Prater page](https://nimbus.guide/prater.html) of the Nimbus guide.