Hadean looks interesting. But there's no documentation available, just hype. Their demo was big, but very simple - it's a FPS in space. They demoed Hadean on Azure, but it's not clear that it's tied to Azure.
The problem is basically distributed cache coherence. You have many small data objects shared between a large number of machines. Often, one needs access to an object on another machine. How do you do that efficiently.
Spatial OS seems to work kind of like a multiprocessor cache.[1] Two machines can have read-only copies of an object. If one copy is changed, the other has to be updated. Performance is better if you don't have to do that too much. They use the fact that they're representing a 3D world to advantage. If something is geographically nearby, they try to keep it on the same machine. To load balance, they will cut up overloaded regions into smaller regions and apply more machines to them, or combine underutilized regions to free up compute resources. This is a rough understanding from reading the documents.
No idea how Hadean does it. The site doesn't say much. It's one of those "onboarding funnel"
sites - no info for you until the marketing people have all your info.
[1] https://en.wikipedia.org/wiki/Cache_coherence#Coherence_mech...