Gaia is the first implementation of the Cosmos Hub, built using the Cosmos SDK. Gaia and other Cosmos Hubs allow fully sovereign blockchains to interact with one another using a protocol called IBC that enables Inter-Blockchain Communication.
Documentation for the Cosmos Hub lives at hub.cosmos.network.
We have active, helpful communities on Twitter, Discord, and Telegram.
With each version of the Cosmos Hub, the chain is restarted from a new Genesis state.
Mainnet is currently running as cosmoshub-4. Archives of the state of cosmoshub-1, cosmoshub-2, and cosmoshub-3 are available here.
If you are looking for historical genesis files and other data cosmos/mainnet is an excellent resource.