A short history of btrfs [LWN.net]
In this article, we'll take a behind-the-scenes look at the design and development of btrfs on many levels - technical, political, personal - and trace it from its origins at a workshop to its current position as Linus's root file system. Knowing the background and motivation for each step will help you understand why btrfs was started, how it works, and where it's going in the future. By the end, you should be able to hand-wave your way through a description of btrfs's on-disk format.
btrfs is a b-tree based fs that is cow friendly (i.e. by removing sibling links you don't have to copy whole tree on block update). Support snapshots, checksums etc. Implementation comes out of Oracle, has some commonalities with zfs.