Docker supports ARMv6/v7 and even ARM64 (v8?), so you can run it on your Raspberry Pis.
Follow the official instructions from Docker here: https://docs.docker.com/engine/installation/linux/docker-ce/debian/
If you have Raspbian Jessie or Stretch (check the above documentation for others), this would be:
$ sudo apt-get install apt-transport-https ca-certificates curl gnupg2 software-properties-common
$ curl -fsSL https://download.docker.com/linux/$(. /etc/os-release; echo "$ID")/gpg | sudo apt-key add -
$ echo "deb [arch=armhf] https://download.docker.com/linux/$(. /etc/os-release; echo "$ID") \
$(lsb_release -cs) stable" | \
sudo tee /etc/apt/sources.list.d/docker.list
$ sudo apt-get update; sudo apt-get install docker-ce
$ sudo systemctl start docker
You can then test it (thanks to Docker multiarch support):
$ sudo docker run --rm hello-world
In order to avoid typing sudo for every Docker invocation, you can do the following extra steps: https://docs.docker.com/engine/installation/linux/linux-postinstall/
Enjoy!
PS: I've installed Ubuntu Server 16.04 for armhf. I have then followed these instructions (for Ubuntu) to install Docker on it: https://docs.docker.com/engine/installation/linux/docker-ce/ubuntu/#set-up-the-repository. It works like a charm as well.