Secure Operating Systems (Microkernels seems to be the future)
I am not satisfied with Linux's security and have been researching alternative open source OS for privacy and security
So far only thing that's ready to use is GrapheneOS (Based on Android) but that's not available on desktop (Though when Android release Desktop mode it may become viable)
Qubes OS is wrapper around underlying operating systems, so it doesn’t really fix for example Linux’s security holes it just kinda sandbox/virtualize them
OpenBSD is more secure than Linux on a base level but lack mitigations and patches that are added to linux overtime and it's security practices while good for it's time is outdated now
RedoxOS (Written in Rust) got some nice ideas but sticks to same outdated practices and doesn't break the wheel too much, and security doesn't seems to be main focus of OS
Haiku and Serenity are outright worse than Linux, especially Haiku as it's single user only
Serenity adopted Pledge and Unveil from OpenBSD but otherwise lacks basic security features
All new security paradigms seems to be happening in microkernels and these are the ones that caught my eyes
None of these are ready to be used as daily driver OS but in future (hopefully) it may change
Genode seems to be far ahead of game than everything else
Atmosphere And Mesosphere Open Source Re-implementation of Nintendo Switch's Horizon OS, I didn't expected this to be security-oriented but seems like Nintendo has done a very solid job
It is a completely unique microkernel with a cooperative (non-preemptive) scheduler. The kernel is secure -- so far as I can tell (as a reverse engineer and hacker), it has zero security bugs. They throw out years of backwards compatibility (they're not POSIX/UNIX), and they really, really benefit from it from a security and modularity PoV.
Horizon's the only meaningful RTOS with a microkernel that I'm aware of (other than Fuschia). Everything's in userland -- filesystems, gpu (and other device drivers). The OS is capability-based and conceptually all about lots of different processes/drivers ("system modules") that host microservices.
The fact that Nintendo designed such a rock-solid, modular, custom operating system for their consoles fascinates me.
IPC is the hottest hot-path in a microkernel, correspondingly Nintendo marked every function involved in IPC as attribute((always_inline)), this was kind of a huge pain to reverse engineer as a result.
In addition, Nintendo implemented "SvcReplyAndReceive" as a single system call that allows a microservice server process to reply to and receive a new message in one invocation.
That said, there's actually less overhead than you think. Past of why FUSE is slower than a kernel driver for FS is because FUSE has to talk to the kernel to do filesystem stuff, so when you read a file you have your process -> FUSE -> kernel -> hardware. In comparison, on Horizon the kernel is completely uninvolved in filesystem management (it doesn't even have the sdmmc hardware mapped). Thus processes will do process -> FS system module process -> hardware.
In Horizon, everything is very distinctly not a file. There's no global filesystem paths the way that unix/linux have special /dev/whatever.
Pipes don't exist in Horizon -- all IPC is done via the horizon ipc ("HIPC") protocol.
UNIX/POSIX have stuff like fork() and child processes...but creating a process is an incredibly privileged operation in a capability-based operating system. Fork() is impossible to implement in Horizon, all threads are created via SvcCreateThread() instead. Child processes aren't a thing that exist.