UPDATE 9.48pm: Facepunch boss Garry Newman clarified, in the commments below, that only 0.04 per cent of revenue from Rust went towards developing prototypes for other projects, such as Riftlight, this year.
Furthermore, Newman noted that the studio's staff consists of 25 people with five working on prototypes of games independent of Rust. None of Rust's devs have been taken off the project to create other games.
ORIGINAL STORY 12.48pm: Rust developer Facepunch Studios has stirred the hornets' nest by announcing a prototype for a new game: an arcade space shooter (with action-RPG elements) called Riftlight, and it's bright and colourful.
Why are people angry about that? Because Rust is an unfinished game - it's still in Early Access on Steam. How dare Facepunch work on a new game when the other one isn't finished yet?
In a blog post written this morning, Facepunch leader Garry Newman addressed exactly that concern, after sharing some rather colourful feedback the company received when Riftlight was announced.
"How you gonna start a new game with the other one not even finished?" enquired one curious mind.
"That's like taking a dump, putting that dump on standby and starting a new one. With the old one still up in there."
Actually it turns out Facepunch has three other prototypes for games in development in addition to Rust and Riftlight.
"Are we crazy?" responded Newman. "Are we doing it wrong? Should every person in the company be working on the same thing? Should HBO make one TV show at a time? Should Warner Brothers make one movie at a time?
"Our strategy at the moment is to hire talented people to make the games they want to play. We're not asking you to fund this. We're not starting a Kickstarter and begging you for money - we're funding it.
"We are spending money Rust and Garry's Mod make to do this. Arguing that we should be re-investing that money back into only those games is like telling Apple they can't spend the money they made from iPhone and Macs to fund the development of the iPad."
Money from Garry's Mod went into making Rust, remember. But why should Rust players be footing the bill for Riftlight?
"We funded Rust for one-two years before it eventually became what it is," answered Newman. "You bought early access to it. When you buy a pizza you aren't funding Domino's, you're just buying a pizza.
"It's true that the sales of Rust have been insane and we have stepped up development to suit, and you only have to compare the experimental version to the live version to see that."
Rust will still be updated "very regularly", as Newman said it is now, and the people who are working on Rust will continue to work on Rust. "They're not working on prototypes. That should be very obvious by the dev-blogs we post every Friday.
He concluded: "I am guessing that a lot of game developers bigger and smaller than us have multiple prototypes in the works, but they aren't showing them to you. The only thing that makes our situation remarkable is that we're willing to talk about our process and show our experiments."