Toshiba has open-sourced GridDB, a Scalable In-Memory KVS
github.com
github.com
Last I checked, there were a lot of Java libraries.
I searched for a shared memory key value store high and low for interprocess communication and the closest thing I found was WhiteDB. WhiteDB is pretty great, but its concurrency is done through locking and it is very unfortunately GPL licensed, which makes it very niche. (BTW a shared memory key value store for IPC is AMAZING).
There are a ton of key value stores out there though amazingly enough I'm still excited when I see announcements because I haven't found one that is what I want.
Or at least Google translate makes me believe it is.