Hazelcast is a small library (363 kb, version 1.5RC1), which comes with distributed, transactional collections and a Java EE JCA (shipped with the zip!). The connector is only needed in Java EE environments to transparently propagate e.g. EJB transactions to hazelcast (outbound transactions).
To install you have only to download, extract and start the sample application (run.bat - it worked perfectly in my case). This should take less than 2 minutes. The installation of the JCA connector is even easier - just drop the hazelcast-ra.rar file into e.g. [glassfish]/domains/domain1/autodeploy/ (I tested the installation only with GF v2).
The screencast (12 min) explains the concurrent, transactional access to distributed collections - well done.
I looked at Hazelcast last year - I liked the ease of use and the quality of the screencast, but not so impressed by the unclear licensing. It was free but not open - and without clear licensing. Shortly after I complained about this fact (no idea whether opensourcing of this library was actually my fault :-)), it changed, now it is a Google Code project with Apache license and so interesting for commercial projects. I guess good support is available as well - at least the main committer answered the question about licensing immediately in my case.
Hazelcast is an interesting foundation for creation of clusters, grids - or "Cloud Computing" :-).