On M2020 documentation, the following exists for additional Timeseries strategies implementations:

https://meridian.opennms.com/docs/2020/latest/guide-admin/#ga-opennms-operation-timeseries

It is Cortex, the one that has had more work in terms of development and stability lately, and it is not mentioned there.

However, none of the existing ones are ready for production, and we officially don't support them. The fact we don't mention this can create false expectations from users (and customers).

JRobin/RRDtool or Newts/Cassandra are the two only official implementations we support. I believe it is good to add a warning on the documentation saying the implementations via OIA are experimental until we can verify they are comparable in terms of performance and stability as Newts/Cassandra is.