Ruderalis is just autoflowering. It doesnt release the flowering hormone judging the dark cycle, instead it judges it's own age and flowers as soon as it's old enough to.

Ruderalis strains are crossed with indicas/sativas for autoflowering plants. [better for beginners]

Eg - Lowryder is an obvious one with Mexican Ruderalis in it.
Some of the skunk strains have ruderalis in them and flower automatically.

Infact, Ruderalis makes growing ALOT easier.