OK, people, here we go! At long last, Multi-System Reactor developer preview is available!
The package can be downloaded from the Reactor bug tracker, a MantisBT system (at https://reactor.toggledbits.com/mantisbt/). There is a download button in the left margin, as well as links to the documentation, which you will need for installation.
UPDATE 2021-02-24 -- To keep spammers off, I've locked down registration on the Bug Tracker. To get access to the Bug Tracker and preview downloads, please PM me (not reply here) your full name and email address and I will set up an account for you.
This version of MSR will run on Linux systems, including RPi's under Raspios Buster, running node.js version 12.10 or higher (v14.15.1). For RPi users, there is an installation script that will install a local copy of node.js (for the logged-in user).
Bugs reports will be handled through the bug tracker only. Discussion and questions in this forum are fine, though (if that leads to a bug report, we'll transition).
This version supports Vera (and openLuup to the degree it's compatible with Vera Luup), Hubitat, and Home Assistant. Some of the device support on the H platforms is still a bit basic, but it is largely controlled by configuration and progress can be made quickly.
The documentation beyond installation is a mess. Of course, I started with the existing documentation and have been massaging into MSR's particulars, but it still has a long way to go on the detail.
I know I don't have to say this, but I will anyway... let me know how it goes!