• nodb - Google Code
  NoDB is a prevalent object repository with indexing capabilities. It is a general purpose in memory repository for use in any Java applications. In a prevalent model, all the objects are kept in memory in native object format. Although NoDB allows to store the objects in a compressed form. The objects stored in a repository can be queried through the use of indexes, so you dont have to iterate over an object graph any more.
  in Software > tools with in-memory java library objects repository

in-memory from all users