qm gem for Ruby includes a
QMachine API server and a web server. It uses
MongoDB for persistent storage, and it can
optionally log traffic data into a different MongoDB collection instead of
logging to stdout. A client is also in development.
Note that support for PostgreSQL, Redis, and SQLite for storage is also available but not recommended for production yet. SQLite, in particular, may or may not wreak havoc when deploying to Heroku, where it presents a number of potential obstacles.
For more information, please see the manual.