PixelMap.io is a big pixel map, consisting of exactly 3,969 tiles. Each of these tiles is either "for sale", or "owned" by someone. The cool part though, is that the ownership, and even the tile data itself is stored on the Ethereum blockchain, which means when someone owns a tile, they are literally the only person on the planet with the power to change or sell that tile from then on (We can't even change it if we wanted to!).
If you're unfamiliar with Blockchain technology, we highly recommend reading up on Bitcoin & Ethereum (the two leaders in cryptocurrency). If you're viewing this website from a normal browser, you'll be able to see the tiles, but you won't be able to purchase or edit a tile unless you're using "Metamask", "Mist", or some other form of Ethereum browser addon that provides Web3 capabilities.
To purchase a tile, visit this webpage from Mist, or from a browser with Metamask installed, then select ANY of the unowned tiles. The unowned tiles are the little grey/white squares. You'll then get a popup window, and for 2ETH, you can be the proud new owner of the tile. After purchasing a tile, wait a few minutes then refresh the page. If you click any of the tiles that you've purchased, you may then "Edit" the tile.
In order to edit a tile, just click any tile on the board that you've already purchased (provided the transaction has gone through, generally taking 30 seconds to a few minutes). You will then be prompted to upload an image, set a URL (if desired), and to set a price. If you leave the price at 0, the tile can NOT be purchased by another user, so don't change the value unless you're wanting to sell it! Please note, that because of the amount of data being stored on the blockchain, it will generally cost between 5 cents to $1 in gas depending on the detail of your image and the length of the URL provided (based on current gas fees).