Firecracker boots up a runtime that has a full blown operating system in it - lambda just happens to call a known program with a known function. In that sense sure it provides similar functionality but it's really quite different. That's not what fly uses firecracker for, for instance.

Qemu/firecracker are in the same space - this is different.

These are most definitely in a different boat as you embed the guest functions inside the host program and then you register those functions. Taken from the readme:

> The host can call functions implemented and exposed by the guest (known as guest functions).

> Once running, the guest can call functions implemented and exposed by the host (known as host functions).

This is more in the 'safe plugin' type of space. As with most things in this space - the best way to learn about them is to simply try it out.