Below is a list of third-party block explorer services displaying statistics about the ETH2 testnet.
beacon.etherscan.io is a beacon chain explorer specific to the Prysm 'Sapphire' testnet.
eth2stats.io is a beacon chain explorer maintained by Alethio.
beaconcha.in is a beacon chain explorer maintained by Bitfly.
Mirrors and Forks
Their respective Github repositories are: