Release 20.1.0 is the latest stable release of OpenNMS.
It is based on OpenNMS 20.0.2 plus additional work done in preparation for Meridian 2017, including a new ReST API to support enhanced OpenNMS Grafana inetgration.
For a high-level overview of what’s changed in OpenNMS 20, see What’s New in OpenNMS 20.
For a complete list of changes in 20.1.0 see the release notes.