Minecraft wiki entry for Development_versions, associated text: Crafted with 6 crying obsidian and three glowstone.
Requires a diamond pickaxe or higher to mine.
Can be used to respawn in the Nether
It is charged with glowstone and can be charged up to four levels. Whenever someone who charged the respawn anchor dies, they respawn near it and the level goes down by 1.
Can be charged with dispensers.
When it is not charged, it does not do anything.
Similar to how a bed explodes in the Nether, attempting to use a respawn anchor in the Overworld or the End causes it to explode.