Notable additions for survival:

Book copying mechanics has been altered to differentiate the original & copies of books
Activator rails can eject entities from Minecarts
Notable additions for mapmakers:

Added a spectator gamemode (/gamemode spectator). Not 100% finished.
Spectators cannot be seen by anybody but other spectators
Spectators can view inventories/etc, but not modify them
Spectators can go through any entity or block without interfering with it
Spectators can click on entities to take their camera
Spectators cannot use items, place blocks, destroy blocks or interact with blocks in any way
Spectators are only slightly buggy maybe sometimes

Bugs fixed in this snapshot:

[Bug MC-38944] – Joining Realms World "Cancel" Button Mis-Placed
[Bug MC-44521] – @a, @e, and any UUID references work incorrectly after a player dies.
[Bug MC-45050] – /fill … skull | Hitbox Bug
[Bug MC-45159] – Blocks with tile entities don't get removed when you clone / fill an airblock to their position.
[Bug MC-45453] – Items & Blocks placed in item frames are rendered incorrectly
[Bug MC-45470] – Items don't render on the ground properly
[Bug MC-45478] – Pre-snapshot14w04a villagers break crops but don't replant them
[Bug MC-45492] – Transparent blocks are much darker
[Bug MC-45554] – Two tall flowers variants are not generating.
[Bug MC-45763] – Some blocks are facing the wrong way if placed in an Item Frame
[Bug MC-45764] – Map will not show in item frame
[Bug MC-45795] – Villagers can not place or pick up any crops
[Bug MC-45847] – /summon Villager Farmer NBT tag canPickUpLoot will default to 0

To get snapshots, open your launcher and press the “New Profile” button. Call it “snapshots” and check the box saying “Enable experimental development snapshots” and save. To switch to the normal version, you can select it in the dropdown at the bottom left corner of the launcher. Back up your world first or run the game on in a different folder (See the “new profile” dialog). Snapshots can corrupt your world, please backup and/or run them in a different folder from your main worlds.

Cross-Platform server jar: https://s3.amazonaws.com/Minecraft.Download/versions/14w05a/minecraft_server.14w05a.jar