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Accumulo is a Java-based key-value store based on Google’s Bigtable. This NoSQL database was created by the U.S. National Security Agency in 2008 and then contributed to the Apache Foundation in 2011. Its distinguishing feature is cell-level access control (instead of database-level or table-level granularity, which is more common), important for fine-grained information security as is helpful for classified materials. Accumulo is in use throughout the Department of Defense, and is presumably still in use by the NSA.
The nature of Accumulo’s applications makes it difficult to determine which agencies that it’s used by, and the extent to which those agencies support it. It is possible that Accumulo is simply open source software that originated within government, as opposed to truly cooperative software.