Linux

crostini is pretty damn great but it's important to know what it IS and it's actually really simple. Crostini is two things combined into one

Firstly A VMM

Crostini uses the crosvm VMM which is can be thought of kinda like an inhouse version of qemu but designed to explicitly run natively integrated and high performance VMs safely instead of being a swiss army knife (KVM acceleration, virtio peripherals etc) (PS. it's written in rust too) They use it for chromeOS to integrate android support (on select newer devices) and linux. It runs a supervisor distro which can run containers inside of it.

ChromeOS calls the VM termina. Im not sure what distro is running in the VM, or if its a specialized one. I forget

Next is the containerization

It is a lot like distrobox, It can run a myriad of distros but the key part of it is sommelier. A wayland compositor designed to render windows through virtio-wayland, an extension of virtio-gpu. In practice very similar waypipe which rendering wayland windows to a remote wayland client using network/sockets (Yes, it does support AV_VSOCK so it can work with qemu.)

Sommelier is run in the containerized Distro, running on the TerminaVM. Using termina provides excelent security and performance, and then using LXD inside of termina provides excellent flexibility

The guts of "crostini" crosvm, virtio-wayland, sommelieris all open source, you can actually (with some degree of hassle) set this up entirely yourself, or do what I do, and run qemu + waypipe for a similar experience. Waypipe is much easier to setup however it comes at a preformance detriment since qemu virtio-gpu perf is worse then crosvm (no vulkan support in qemu yet still)

EDIT: s/Architecturally/in practice/ I have no idea why I said Architecturally. they are quite different things. I must have had a brain fart