Centuries ago, armies discovered that soldiers performed better if they slept under shelter, and began issuing individual tents to be carried on the march. Inevitably, soldiers began wrapping their tents around them as shelter from the rain as they walked. Commanders took notice, and modifications were made so that the tents would be more useful as cloaks.
These are what evolved by the early 1900's. They're more effective than ponchos, and more convenient and versatile than rain suits. I've collected German, Swiss, French, Swedish, Norwegian, Hungarian, Czech, and now Polish versions. The latter is the best of the best.