The ethereum 2.0 Medalla testnet has five node clients, but just one of them is being used by the vast majority of nodes. Despite a week long network crash in August due to a small bug in Prysm, that client is still being used by some 60% of the network. The second most popular client is Lighthouse with just 36 nodes out of 155, making it 23% according to our own research based on eth2stats. Teku has 15 nodes out of 155, less than 10%, with Nimbus at nine and Lodestar at just two.