Operating system: Linux, with the libcless linux-none target
Target: LoongArch (LA32R, LA32S, LA64)
Target: Rust from the parallel universe where the Amiga won.
OS: QNX Neutrino, a POSIX-compatible real-time operating system
Operating system: NixOS, https://nixos.org/
Target: the NVPTX LLVM backend for running rust on GPUs, https://llvm.org/docs/NVPTXUsage.html
Operating system: OpenBSD
Target: PowerPC processors
Operating system: Redox, https://www.redox-os.org/
Operating system: RISC0 zkVM https://risczero.com/
Target: RISC-V architecture
Operating system: Solaris
Target: SystemZ processors (s390x)
Target: Arm's secure enclave that code isn't supposed to be able to jailbreak
Operating system: trusty (https://doc.rust-lang.org/nightly/rustc/platform-support/trusty.html)
Operating system: tvOS (including simulator)
Operating system: Unix-like
Operating System: Sixth Edition UNIX from Bell Labs
Windows targets for Universal Windows Platform (UWP) applications, using MSVC toolchain.