Comment by ducktective

QNX was a true microkernel architecture that worked, and worked well. The basic building block was called IIRC Send/Receive/Reply: Every "system" call looked like a regular function call, but would "Send" a message to a different process, and (usually) suspend the caller; The other process would "Receive", do whatever was requested, and "Reply", at which point control went back (with the response) to the calling process. IIRC it was also possibly to do async calls, but in that case the other process would call ("Send") the response back, rather than "Reply". I might be confusing this with another system though.

device drivers weren't privileged - they were just another process you called into, and could be restarted in the case of a fault (rather than kernel panic or blue screen).

A system that doesn't provide this is not an alternative to QNX; It's just another operating system (which are all, in some ways, alternative to each other and thus QNX, but ...)

1. Nothing. Someone was writing a QNX-type kernel in Rust. What happened to that? There's L4, but it's too low-level. It's more of a hypervisor. People usually run another OS, usually a stripped-down Linux, on top of L4. QNX offers a POSIX API, so you can run applications directly.

2. C++. Here's the source code. [1]

3. No.

[1] https://github.com/John-Nagle/Overbot/

>What's the FOSS alternative that is as good as QNX nowadays? FreeRTOS, NuttX, Zephyr etc are used for MCUs not general purpose computation AFAIK

SeL4 with CAmkES, or Genode.

In automotive infotainment systems, where QNX was used a lot in the past, it mostly had been replaced with combinations of Linux or Android on the non-realtime critical systems, and smaller microcontrollers which run realtime OS (OSEK and autosar derivates). The latter are usually not open source.

Dunno if it’s an alternative but Linux had RT_PREEMPT and you can build a kernel that’s fully preemptable.

Minix 3 is closest to "as good as" minus the realtime support.