MirageOS is a library operating system that constructs unikernels
Since you're focusing on server-side applications, you might be interested in Mirage OS. It's a project that constructs minimal application-specific VMs constructed using OCaml. Haven't used it but I believe the idea is you write your service in OCaml, test it on a normal system, and when you're done it will build a minimal VM image that has the minimal amount of OS required to host and run the service. You then manage it with xen or kvm.
What advantages does applying type-safety to OS give?
1 project | reddit.com/r/osdev | 9 Apr 2022
Crash-Only Software and Recursive Microreboots
1 project | news.ycombinator.com | 29 Mar 2022
2 projects | news.ycombinator.com | 11 Feb 2022
writing kernel in haskell or ocaml.
1 project | reddit.com/r/osdev | 26 Oct 2021
Why should I learn OCaml?
1 project | reddit.com/r/ocaml | 9 Jul 2021