rnDB

RnDB is a procedurally generated fake database. You define tables with columns whose values follow a given distribution or come from a generator, choose a random seed and a record count, and query it as if it were real. It can simulate a trillion records without storing any of them, because each record is generated deterministically on demand.

It’s handy for testing, demos and games that need a large, consistent world of data. The blog post The Case of the Fake Database and the video overview explain how it works, and it’s published as a Ruby gem.