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Modern kernels - be they UNIX or Unix-descended (BSD) or Unix-like (Linux), or similar to modern POSIX in features/memory/process/threading but different in API (NT) - are good enough for almost all modern applications. With modern hardware, even niche/embedded/real-time applications can run on variants of these kernels.
The real innovation in the past decade or two has been in virtualization
1 2. The same boring old kernels can run on top of virtualized hardware and a running system image can be migrated between disparate systems and capacity can be added/removed as necessary. This is really just an extension of the virtualized environment in which processes run on top of a modern operating system kernel - aided when possible by hardware (with the most recent x86-64 CPUs), but doable with software patching with acceptable performance (on x86). Still, the ability to have a single virtualized system image and be able to hot-add RAM, CPU resources, and to be able to migrate it to systems across great distances with no noticeable impact on the applications running in the OS is amazing.
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1for the most part, virtualization isn't really a recent development, although on x86(-64) and other commodity hardware it may seem to be. it's mostly stuff IBM had on their ENTERPRISE systems by the 80s afaict.
[sub]2to be fair, some innovation did occur in related spaces - composited 3D accelerated desktops are now standard on any respectable desktop operating system. advanced filesystems like ZFS exist, and others like brtfs are in development, although they really just implement stuff that
ENTERPRISE systems with VxVM/VxFS, netapp, etc. had in the 90s.