Intel Labs built a tool for constructing mathematical graphs out of large datasets. It is Java based and works with Hadoop and MapReduce. Intel has release a whitepaper explaining more about GraphBuilder. The code is available on Github. A big thanks to Mark Nickel for pointing out this project.
ArangoDB is a flexible NoSQL database. It is a document database with the ability to add edges. Thus it can become a graph database. I had a fun time playing around with the online tutorial and demo. ArangoDB also claims to support being a key/value store. The code is available on Github.