To be clear, #[no_std] only "removes" the runtime by ensuring you don't accidentally use any functions that need the runtime. Something like

  #![crate_id="basic_lib"]
  #![crate_type="dylib"] // for a .so

  /* not there's no `no_std` */

  #[no_mangle]
  pub extern "C" fn add_in_rust(x: i32, y: i32) -> i32 {
      x + y
  }

Compiling that will give a `libbasic_lib....so` which can be linked against by any C program, and the `add_in_rust` function called without the Rust code needing to touch a runtime. (I imagine that one may have to add some extra linker flags.)

There are many functions/types in libstd etc. that can be used without a runtime (although its still not as great as it will be in future).