Java In-memory Query Language (JIMQL) allows SQL like query and join operations on Java collections.
The project is influenced by Microsoft's LINQ, as well as similar Java based implementations.

The code is distributed under an open source license an is available on Google Code

The motivation for the project is contained in the following two articles
Review of Efficient Object Querying for Java
Using an In-Memory Database for Efficient Querying of Java Objects

At this point, JIMQL is still a work in progress, though portions of it have been used successfully in real world projects.No official release has been made and is planned. I would love to hear any comments on the ideas and goals of JIMQL.