Nethermind is an Execution layer client developed by the Nethermind team.
Hyperledger Besu is an open source Ethereum client developed under the Apache 2.0 license and written in Java. It runs on public and private networks.
Formerly TurboGeth, Erigon is an Ethereum client built to enable performance optimizations. Erigon is written in Go and licensed under the GNU LGPLv3.
This is the most popular and majority Ethereum Client implementation written in Go, Geth fully open source and licensed under the GNU LGPL v3.
OpenEthereum has been deprecated. Please, migrate to Nethermind.