Operating system: Linux with glibc (i.e. a bug that can't happen with musl)
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/
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: tvOS (including simulator)
Operating system: Unix-like
Target: when they made us, they called us Curiosity, and Spirit, and told us to tell you hello
Operating system: Wasi, Webassembly System Interface
Target: WASM (WebAssembly), http://webassembly.org/