One of the inherent drawbacks of digitally distributed games is that you can't loan them out to friends, but Steam has rewritten the rules a bit. Now that Valve's Family Sharing feature is out of beta, pretty much anyone can authorize another user -- that they trust with their account and its attached reputation/information -- and their device to "borrow" a game from their library. It's taken a few months to happen, but if your best Steam buddy owns Rust, you should finally be able to give it a shot before plunking down the cash for it yourself.