You let the host manage memory, disk, network etc and your program is a [process] that doesn't need all the extraneous processes that usually go with a whole OS. No background services or cron jobs.
So it's like Docker.
So it's like Docker.
Docker/cgroups/namespaces allow you to isolate multiple applications running in userspace on the same kernel to a very high degree.
This gets rid of isolation and multiprocessing altogether and runs a single application without any kernel at all (i.e. with just a very limited amount of support code linked in).
Put simply; the technology behind docker improves isolation between processes and this does the exact opposite.