I believe early on Linode used UML for their VPS hosting offering. At that point in history, I recall solutions like OpenVZ being pretty popular in the low end space, too.

gVisor's modular design seems to have been its strongest point. It's not that nobody understood the OS is just software or whatever, but actually ripping the Linux TCP stack out and using it in userland isn't really that trivial. Meanwhile though a lot of projects have made use of the gVisor networking components, since they're pretty self-contained.

I think gVisor is one of the coolest things written in Go, although it's not really that easy to convey why.

Seriously, just check out the list of packages in the pkg directory:

https://pkg.go.dev/gvisor.dev/gvisor

(I should acknowledge, though, that I don't know of that many unique use cases for all of these packages; and while the TCP stack is very useful, it's mainly used for Wireguard tunneling and user mode TCP stacks are not particularly new. Still, the gVisor network stack is nicer than hacked together stuff using SLiRP-derived code imo.)