SMACK - low-level IO storage which packs data into sorted (zlib/bzip2/snappy compressed) blobs
It was created to host huge amount of rather small compressible data in elliptics,
thus providing extremely fast write performance (tens of thousands RPS per node with hundreds of millions already written objects),
backend architecture was implemented with HBase in mind, but some changes were tested and made different.

Origianlly created as backend for elliptics: http://www.reverbrain.com/elliptics/
Benchmarks: http://www.ioremap.net/node/541

Smack: http://www.reverbrain.com/smack/
Google group: https://groups.google.com/forum/?fromgroups=#!forum/reverbrain