As far as I know, Azure Durable Functions doesn't have a server-side proprietary component and it's actually fully open source framework/clients as well. So it's actually not a cloud offering per-se. You can see the full implementations at:

* https://github.com/Azure/durabletask

* https://github.com/microsoft/durabletask-go

That's interesting, I'll take a look! I had always thought of it as an Azure-only thing.