There is a great deal to love about RChain – especially that it is a cooperative venture first! I keep looking for a project to dive into with them. <3
The team did mention having a testnet here https://www.dsnp.org/testnet – not sure of the status beyond that? It is mentioned in an update post here too Developer Update - May 2021. Hopefully someone in the know can chime in. I also believe a protocol is best developed in the open and assumptions tested against working code.