The Nile Testnet is an Ethereum Proof-of-Authority (PoA) network where all the nodes (Keeper nodes) are running Parity Ethereum. There are two kinds of Keeper nodes in the Nile Testnet: authority nodes (voting nodes) and user nodes (non-voting nodes).
Authority nodes have a say in determining which transactions are valid. In the Nile Testnet, the authority nodes are run by BigchainDB GmbH and its partners. If you’re interested in running an authority node in the Nile Testnet, then email [email protected].
Anyone can run a user node. It will stay in sync with the other nodes in the Nile Testnet, it just won’t have a say on whether transactions are valid. Marketplaces and publishers should run user nodes. See the pages for marketplaces and publishers.