We run FaunaDB as a service, or you can license it for on-prem use. Drivers and tooling are all open however, and we plan to release the source for correctness testing as well.

Our property tests are written in Scala as a Monad for controlling execution and random sample generation, and our internal distributed test harness uses Akka. This worked out nicely because we were able to make the relevant integration and fault tests scale from local runs via SBT to full geo-distributed clusters and OS-level fault injection.