Bigdata(R) is an open-source scale-out storage and computing fabric supporting optional transactions, very high concurrency, and very high aggregate IO rates. Bigdata was designed from the ground up as a distributed database architecture optimized for very high aggregate IO rates running over clusters of 100s to 1000s of machines, but can also run in a single-server mode. Bigdata offers a distributed file system, similar to the Google File System but also useful for workflow queues, a data extensible sparse row store, similar to Googles widely recognized bigtable project, and map/reduce processing for parallelizing data intensive workflows over a cluster. Bigdata(R) comes packaged with a very high-performance RDF store supporting RDF(S) and OWL Lite inference. The Bigdata RDF Store is currently the only RDF database capable of operating distributed on a cluster with dynamic key-range partitioning of indices. The Bigdata RDF Store was designed specifically to meet requirements for very large scale semantic alignment and federation. RDF is a Semantic Web technology particularly well-suited to modeling graph-shaped data and metadata, such as an associative entity-link model, whereby actors are linked to one another in an ad-hoc fashion within the context of an evolving ontology of concepts for entity types and link types related to a particular problem domain. The Bigdata RDF Store is used operationally in data harvesting systems to create mash-ups of structured, semi-structured, and unstructured data from myriad sources in a schema-flexible manner.

Hazelcast is an open source clustering and highly scalable data distribution platform for Java.

nmdb is a network database (dbm-style) for controlled networks that can use different protocols to to communicate with its clients. It supports TIPC, TCP, UDP and SCTP. It consists of an in-memory cache that saves (key, value) pairs, and a persistent backend that stores the pairs on disk. Both work combined, but the use of the backend is optional, so you can use the server only for cache queries, pretty much like memcached.

Distributed and persistent key-value database

High performance BDB-like in-process key-value DB. Has master-slave replication, multi-master, remote server, and full-text search with bindings for Java, Perl, Ruby, etc.

Neptune is Distributed Large scale Structured Data Storage, and open source project implementing Google's Bigtable. Hbase-like.

Parhely is an ORM system for HBase. It as well contains some utils such as AbstractShardedDao which can be used to shard MySQL db's for instance.

Mammatus's main focus is to deliver various cache and storage solutions which each addresses common challenges. All implementations follow the java.util.Map interface which makes it very easy to plugin.

Cassandra is a distributed storage system for managing structured data while providing reliability at a massive scale.

Cloud storage and CDN optimized for large files. Comparable to Amazon's S3.

High-level abstractions or data structures as the fundamental storage infrastructure