Minecraft 1.8 allows players to create a flickering border in their world. The Farlanders have used this feature to great effect in a new survival gametype called Captive Minecraft.
At the start of Captive Minecraft, you're in a 1x1 box. The world border blocks your movement. However, there's a way to push these walls back: earning Achievements.
"For each Minecraft Achievement you get, the World Border widens by half a block in each direction," the creators say. "As your captive world slowly expands, you gain access to more and more resources. You'll have no trouble Getting Wood or Taking Inventory, but suddenly making that Cake and riding a Pig off a cliff isn't quite so simple..."
You have more room to manuever than you expect. The borders apparently don't prevent you from moving vertically so you can start digging downward to find more resources.
Captive Minecraft uses a custom map rather than randomized worlds. This ensures that you'll have a fair chance at advancing and won't just get screwed by chance. The creators included some "fail safes" just in case something unexpected happens. For example, chickens die immediately when they hit the borders due to a bug.
Like most things in Minecraft, the gametype is better with friends. This doesn't necessarily make things easier, though. While multiple players can earn the same Achievement, the Achievement will only expand the world borders the first time it's earned in the game. Holding Tab lets you see who has contributed the most Achievements to your group's success.
The Farlanders mentioned some important details on Captive Minecraft's website. They recommend holding off on going into the Nether before you've expanded the world borders a great deal, because the borders are eight times tighter there. Additionally, they advise you to relog if you die too often. Visiting the End currently renders you unable to move. Also, don't cover up the first Quartz Block in the world some some "friends" will come to visit.
You can download the beta version of Captive Minecraft at the Farlanders website. Minecraft 1.8, the patch that introduces the world border feature used in the mode, isn't out yet. However, you can still play the game type by downloading snapshot 14w18b or later for that patch.