This is a map for Minecraft 1.6 snapshot 13w25b and above, this is not a mod and uses only Vanilla Minecraft features. It provides basic functionality and you are still expected to manage some things yourself.
How it works
The recent snapshots have added a new potion effect that changes your maximum health based on the effect level. Stepping on a pressure plate will activate a command block that grants this effect to all players indefinitely.
The map is infinite daytime, there is no day/night cycle and the sun is always in the middle of the sky. This is using the new gamerule that disables day/night cycle, no laggy redstone clocks are used in the map.
In singleplayer, your fist does 1 heart of damage instead of half a heart. In multiplayer, it does half a heart (there's no way around this, sorry).
Download includes a singleplayer ave file and a multiplayer server (does not include server jar or exe, the txt file has a link to the official download).
I updated it to v2 after I learned about how to properly use scoreboards. Now health is displayed on the tab screen and kills are displayed on the right side of the screen (only for >0 kills). The health display is buggy due to Minecraft bugs, it starts displaying at 0 until it changes. Each 1 point is half a heart, so 20 is 10 hearts and 40 is a full 20 hearts.