The most common [reason] why applications scale-out [is so bad], [is due to] the database. [The] database is the bottleneck of most of applications. OrientDB scales out very well on a single machine. A single server [of OrientDB handles the same] work [as] about 125 servers running MySQL. -- OrientDB Project
It's surprising to find that the project's long history still hasn't culminated in a production-ready tool (according to Alex Popescu, OrientDB is still considered experimental).
According to the Orient website, the original engine was developed in C++ back in 1998, and has since grown into its new, "totally rewritten" Java version. This new version combines features from an array of sources, including Object Databases, Graph DBMS and cutting edge NoSQL engines. This results in a very fast, easily installed DBMS. For those wanting to learn more about OrientDB, the team has put together an in-depth wiki.