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Off the top of my head here are three different offerings from Microsoft that enable cross cloud applications: - https://azure.microsoft.com/en-us/services/azure-arc/ - https://dapr.io/ - https://keda.sh/

The runtime for their serverless functions is also open source and (I guess) fairly portable: https://github.com/Azure/azure-functions-host

That's pretty cool not an expert so can't know how truly portable it is, or is it like "Visual Java" ;-)