I'm not sure if this system is a good idea or not but I wish some commenters would spend more time comparing their proposed solutions (shared mem, local db, memmap...) to Hammerspace rather than contentless dismissal.
Comparison to local dbs like cdb, sparkey, mapdb, gettext files etc. -- hammerspace is a gem that uses sparkey under the hood, so these solutions are more or less one and the same. The difference is that hammerspace exposes a ruby hash-like API to make integration with existing applications easier. It also provides concurrent writer support, which many local dbs don't do.
Whether it's a good idea or not is for you to judge -- we've open sourced the gem in hopes that it will be useful to someone, just as sparkey and gnista were useful to us.
It seems like some of the criticism in this thread comes from people who haven't bothered to understand what you've done and summarily dismiss it as stupid. That attitude has been bothering me lately on HN or maybe its programmers in general.
Anyway, thanks for the interesting contribution.