Stereum

staking-deposit-cli generates validator keys and deposit data for Ethereum staking, and is now maintained as the EthStaker fork that the original owners point to. Validators run it once when setting up new keys.

Besu is a Java Ethereum execution client hosted by LF Decentralized Trust, formerly under Hyperledger, with wide enterprise use. Node operators run it when a deployment is standardized on the Java stack.

Teku is a Java Ethereum consensus client from Consensys that is favored by institutional operators. Validator and node operators run it when a deployment is standardized on the Java stack.

Ream is a Rust implementation of Ethereum's proposed Lean Consensus design. Client developers use it to experiment with the next consensus architecture, and it is not a production node client.

Nethermind is an Ethereum execution client written in C# and .NET, and the second most used client on the network. Node operators and infrastructure builders run it to serve JSON-RPC and follow the chain.

Erigon is an efficiency-focused Ethereum execution client that embeds the Caplin consensus layer. Infrastructure builders run it when they want one process for execution and consensus and fast access to historical state.