Tux3 is a versioning file-system that was announced a half-decade ago to replace the Tux2 file-system that had licensing/patent issues. Tux3 was re-announced at the start of 2013 and proves to provide competition to EXT4. Since then it gained initial FSCK support and performance improvements while there's also been talk of design improvements for the open-source file-system.
Daniel Phillips is the creator of Tux2/Tux3 and is working at Samsung Research America. Back in September he presented at LinuxCon North America on the state and future of Tux3.
Among the modern features of Tux3 include the use of extents, file index as a btree, inode table as a btree, variable-sized inodes, variable number of inode attributes, and unrestricted metadata position. Daniel for Tux3 is also working on new atomic commit, indexing, and versioning technologies for the file-system. Among the advanced work of Tux3 is delta upgrades and page forking, an async front/back-end, log/unify commit, shardmap scalable index, and versioned pointers.
Among the features Daniel Phillips is wanting to take care of before merging Tux3 to mainline is proper allocation support to resist fragmentation and "ENOSPC" error no space support for having robust full volume behavior. After the code is merged to the mainline tree, features to be tackled include repairing FSCK, shardmap directory index, data compression, and versioning/snapshots.
The Tux3 file-system update as of last month can be found on the Linux Foundation web-site in PDF form.