I know that NTFS supports encryption but otherwise is closed source. Likewise, I am aware of add-ins such as truecrypt but I am interested in encryption being built-in vs being bolted on.
Keep in mind that encryption is often not done at the filesystem level. It's done at the block level, where sectors are actually read/written to disk. This allows one to use any filesystem with the encryption, as the filesystem sits on top of the encryption layer.