This is the first snapshot of the 1.8 update. It adds such dangerous ideas as stackable doors, 3 new block types, recipes for mossy bricks, and new rules for Adventure.
There’ll be no more breaking / placing blocks if you’re in Adventure Mode, although that could change with a little command or two. Snapshot 14w02b changelog.
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!