Yahoo! presented Omid at Microsoft Research Silicon Valley, in which the top researchers are working on efficient support of transactions on top distributed key-value stores. Moreover, Yahoo! presented Omid at major hadoop players, Cloudera and Hortonworks.
Omid is the open source project released under the umbrella of CumuloNimbo (https://github.com/yahoo/omid/). Omid provides transactional support on top of distributed data stores including HBase.