World Painter Minecraft World Creator / Editor Tool
A tool still very much in the alpha stages, World Painter is a tool that allows you to create your own Minecraft worlds from scratch. Think of it like MC Edit, but instead of having to work your way through three different dimensions, you can just paint layers onto a topographical style map. Having used both MC Edit and World Painter, I find World Painter to be more intuitive and much easier to use than MC Edit.
This isn't suitable for precise work, you're not going to be able to build the Taj Mahal brick by brick in this program, at least, not yet, but it is wonderful for creating landscapes to order. Want sweeping plains with rivers running through them and mountains rising in the distance? No problem. You have control over biomes, the spawning of ores and minerals, even the population of animals.
There are a series of terrain tools that allow you to flatten terrain, raise terrain, flood terrain with water and lava, place the spawn point wherever best suits your purposes, create pyramids out of nothingness, spawn forests at the click of a button and so much more. As the tool is developed over time we can expect to see more functionality. At present time, for instance, it is possible to raise mountains but not possible to dig ravines. Ah well. One cannot have everything delivered to one on a silver platter carried by a well dressed man from Montreal, can one?
Because this is still a work in progress, it helps to download the tool and play with it then offer feedback to the developer. I think that at the present stage it makes a nice compliment to MC Edit, or a wonderful tool for anyone who wants to make a particular type of landscape. Want a world of sandy dunes? That is within your power. You can even paint in oasis and other resources if you want a place to water your camel. (Camels not included.)
The caverns function allows you to infest your world with underground (and above ground) cavernous structures. If you're wondering what an above ground cavern might look like, it's one of those megalithic dirt and rock structures that tower into the sky in great arches, simulataneously ponderous and awesome.
There's also a 'biomes' button, which takes the information from the seed of the world you're working on and shows you where various biomes are. (Yes, that's another benefit of this tool, the ability to define specific seeds up front, generate a world based on them and then edit it after the fact.)