Service fabric from Microsoft comes to mind but it is not open source.
I migrated a decent sized solution still in dev from SF to .netcore and SF - 10/10 would do it again. Not to mention that you also end up saving 50% $$$ on vm costs with linux vms (not considering SF on Linux)
Do you recommend using SF or not? you mention that you would do it again - was that only about moving from Windows .NET to .NET Core on Linux (ie. NET Core rocks?) and the rest about SF is crap or would you recommend SF in general for any future work (instead of for example Akka.NET for service coordination in a cluster) ?