Update: Snapshot 14w26c has been released to fix broken block IDs, world generation in the nether and the end and some more bugs.
If you are updating from 14w26a or 14w26b, your saved world has corrupted blocks and it will be heavily damaged once you open it in 14w26c. Please use a world backup that was saved with a pre-14w26 version.
Never use snapshots without first making backups of your saved worlds.
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/14w26c/minecraft_server.14w26c.jar
Cross-platform server windows exe: https://s3.amazonaws.com/Minecraft.Download/versions/14w26c/minecraft_server.14w26c.exe
Credits: Mojang Team