If you had to imagine all the uses for the Ethereum blockchain, it's a safe bet to say you wouldn't have come up with a game based on collecting digital cats. Further to that, even if you had come up with that kind of idea, it is probable that many would not have deemed it a big money-making scheme.What's surprising then, is that this is what has actually happened in real life! Game makers AxiomZen have seen their creation CryptoKitties become wildly popular since its launch. This has led to over $1 million in user spending when the game transactions have been analysed.For anyone who has never come across it before, this game is based on collecting in-game cats. Originally, 100 starter kitties were created and, since then, a new Gen 0 kitten is added into the game every 15 minutes. Users buy these cats using Ethereum and this is where the spending comes in. With the basic new kitten going for around 0.3ETH (or £10.50), one of the original 100 have been known to fetch 246ETH (or a whopping £86,000!) Once you own a kitten, you can keep it or sell it via an in-game auction. This is where a lot of users make their money, as the price they sell at can be much more than they paid at first. You can even hire your kitten out for breeding if you like!The popularity of this game is based on people's love for animals and collecting things. One advantage it has is that, as it is based on Blockchain technology, the kitties you buy are 100% yours to do with as you please. Obviously, the other attraction for the player is the prospect of making big money by selling your kitten or hiring it out for breeding purposes.It is perhaps a little odd that this is the big news around how Ethereum can be used! The figures don't lie though and, with this game accounting for around 15% of the Ethereum network, it looks like it's here to stay. As the popularity of the game grows, it will be interesting to see how the network handles more and more users.