While technically not a mod, the map is a drastic departure from the basic mechanics of Minecraft and to my mind introduces game play that is so radically different that is deserves status as a ‘Mod’.
When you start this map you are greeted with this.
In the chest is some lava and ice which you can use to create infinite cobblestone (Which you still have to mine manually. This isn’t redpower). From there you simply build. In the distance is a precarious sand island with some obsidian and seeds. The sand has a tendency to fall if another block touches it (at least in my experience) so I had to build a platform beneath it before plundering it’s goodies.
After about two hours I managed to complete this. Click the image for a higher resolution picture to see more details.
Here is a cactus farm on the left (I realize it serves no purpose as all the sand I have is here and I can only replant cacti on sand.). You can sort of make out a patch of grass in front of the ramshackle house as well. It is all the dirt I have and so far looks like it is too small to spawn any animals sadly. On here is also a melon and pumpkin farm in a strip on the left. Next, with a partially burnt down roof is the cobble stone generator where I get my materials for cobblestone and stone bricks as well as my crafting bench and furnace.
Finally my tree farm which I use to power my furnace and as a building material. Six seemed to be enough to keep me in more wood then I can reasonable use so I stopped there.
From here I need to make a mob farmer to try and get iron drops from zombies (5% drop I think) and maybe some string from spiders to make a bow. I also need to figure out how to get animals to spawn so I can make some leather armor and a better source of food.
My biggest problem is I don;t know where to get flint to make a flint and steel for the nether portal as I have ten obsidian.
If you are curious then you should check out http://www.skyblock.net for more details and the forums. They have online servers with some more functions like trading and a place to farm animals and mobs easier.
Personally I like the desolation of being alone ^^.