For those not familiar with LessFS since it's not nearly as popular as EXT4 or Btrfs, it's self-described as "a high performance inline data deduplicating filesystem for Linux." In part what makes this file-system less popular is that it's based upon FUSE -- the file-system in user-space project that Linus Torvalds says is for toy file-systems and misguided people. It's also a bit interesting the developers chose to go with FUSE as this file-system is designed for "high performance" purposes under Linux.
Besides offering up de-duplication support, LessFS also supports compression. QuickLZ and LZO compression support is handled while back in September they introduced support for Google Snappy (the announcement). When using LessFS with Snappy compression instead of QuickLZ, the time it took to transfer a software ISO to the FUSE file-system was cut in half, according to the project.
Earlier this month LessFS 1.6.0 reached beta (the announcement). This latest version features a functional multi-file I/O back-end, compiling with BerkeleyDB as its database back-end rather than TokyoCabinet, and the batch replication feature has been "extensively tested and improved." The developers mention that LessFS 1.6 will mark the end of new feature releases with just future versions being bug-fixes, presumably to begin work on LessFS 2.0.
LessFS is licensed under the GNU GPLv3. For those wishing to learn more about this FUSE file-system that supports Snappy compression and data de-duplication, visit LessFS.com or the SourceForge site. Another open-source Linux file-system supporting de-duplication that's built on FUSE is Opendedup SDFS.