So, to lay it all out there:

In the beginning, there was multirust. This was a bash script, or rather, a set of them, I guess. It didn't really work on Windows, though, being a bash script.

Then came multirust-rs. We already have a programming language that we like to write that supports the platforms Rust supports: Rust! So, port multirust to Rust.

Then, it was decided that mutlirust-rs would be the right path to move forward generally, so a plan was formed to figure out just exactly how we'd want such a tool to truly work, rather than just copying what multirust did, and so this became rustup.

https://github.com/rust-lang-nursery/rustup.rs is the repo.

The setup tool and the tool itself are the same binary. The rustup install is basically copying rustup-init.exe to `~/.cargo/bin/rustup.exe`.

This blog post is sort of like a bigger beta announcement, to get things in front of a larger audience and make sure things are still good. It will be the recommend way to install rust soon, but not quite yet.

I do recommend using rustup to all Rust developers now, despite still having reservations about its done-ness, and not being ready to commit to putting it on the main website (I guess that's something of a contradiction).

This blog post marks the beginning of the phase where we will seriously try not to break things on upgrade - I consider it 'in production' now.

Even now I think it provides the best installation experience and I have much higher confidence in its reliability than the older multirust shell script.

That said, if you are on Windows you might want to be more cautious. Just this week I broke rustup's networking on Windows, and there are periodic reports of intermittent self update failures (though these don't cause data corruption).