I used a couple of gems to work with Redis key-value store (redis-objects, dm-redis-adapter with dm-core, ohm) but all of them have some drawbacks (even ohm does not have polymorphic associations yet), so I decided to write an ORM for Redis.

redis_orm is compatible with ActiveRecord’s 2.x API (: It supports belongs_to/has_many/has_one, has_many/has_many (HABTM), self-referencing and polymorphic associations, it uses ActiveModel for validation. Also it has create/save/destroy callbacks and indices (to find records by their value rather then to quick access them), dynamic finders and dirty methods (property_changed?/changes). To spawn and kill redis-server properly all tests are written in RSpec. More: source, gem, issue tracker