A team of ex-Googlers is building an open source version of Google Spanner, i.e., a transactional database that spans across many data centers.
GoogleSpanner is a globally-scalable database system used internally by Google; it is the successor of the BigTable database. The database supports SQL-like queries, implements transactions, is distributable among many data centers, and is fast. The paper describing the technology published by a team of Googlers in 2012 caused quite a stir in the community since it managed to marry features that were thought to not be possible to combine together (e.g., see Hight Scalability blog or Doug Cutting's statement that Spanner-like technology should be the next step in Hadoop's evolution (see the clip with him where he talks about Hadoop's evolution - the interesting part starts at 5:50)).
Now, as reported in a recent article at Wired, a team of ex-Googlers is developing an open source version of the Google Spanner called CockroachDB. However, the team does not plan to implement all the features of the original solution in the first version of the project. Currently, their focus is on automatic replication of data between data centers and assuring lack of dependency of the solution on any particular distributed file system or system manager. According to the article, the project is in "alpha" development phase and is "nowhere near ready for use with production services."