Longevity is a persistence framework for Scala and NoSQL. It was originally built with a MongoDB back end, but I've always planned on supporting more kinds of databases. Longevity is mature enough at this point to add a second back end, and I chose Cassandra for a few different reasons.
I recently worked with Cassandra on a contract position, and while I can't say I came to love it, I did come to understand it. It's the second NoSQL database that I've had substantial experience with, which makes it an easy choice.
While they are both NoSQL databases, MongoDB and Cassandra are very different. I decided it would be useful to have a Cassandra back end sooner rather than later, to avoid overfitting longevity to MongoDB and similar databases.
Finally, Cassandra has great market share.
If you're doing Scala and NoSQL, please take a look! A good place to start is the Getting Started Guide, which will give you a feel for how it works. If you want to go into more depth, take a look at the user manual. The manual is not fully complete yet, but all the core functionality is well covered there.
I'll be focussing on a small handful of API fixes and improvements for the next release. I'm tempted to move on to adding some more missing features, but I want to do things right and not accumulate technical debt, so the new features continue to be easy to implement.