Mojang has released a new Snapshot for Minecraft today. This is the Minecraft Snapshot 14w02b and here is what it includes.
The first snapshot of Minecraft 1.8 has arrived! This update will be split into two primary focuses: Survival gameplay & improvements, and new fancy abilities for adventure maps! We’ve done a whole bunch of optimizing for both the client and server (with more to come!) and lots more work towards the Plugin API in the background. As this is the very first snapshot of 1.8, do remember to backup your worlds before trying it!

Big survival changes:
  • 3 new stone types!
  • Major Enchanting & Repairing changes!
  • Mossy stone bricks recipe!
  • Updated Villager trading!
  • Doors stack!
  • Slime blocks!
  • Lots of other tweaks, changes, bug fixes and secret features!

Big Adventure Map changes:
  • Adventure Mode no longer lets you place/destroy blocks.
  • But that can change!
  • Added Entity Selectors! Use @e in certain commands to target entities. You can limit it with [type=Chicken] or [type=!Skeleton]
  • Added a /blockdata command!
  • Added ‘Lock’ (String) NBT tag on most containers.
  • Added an optional entity parameter to /kill (try: /kill @e[type=!Player]
  • Added optional arguments to /clear for max item count (use 0 to not actually delete anything) & NBT data
  • Lots of other tweaks, changes, bug fixes and secret features!

Running a Snapshot release is as easy as:
  • Open your launcher
  • Press "New Profile" button
  • Name it "Snapshots" and save
  • Be sure to make a back up of your world saves just in case you feel like reverting back