Open source, zlib licensed
What Portainer does and why run your own
Portainer is a management UI for containers. It sits on top of Docker, Docker Swarm or Kubernetes and gives you a web view of everything running, plus the logs, volumes and networks behind it. The Community Edition is free under the zlib licence and ships as a single container you point at the Docker socket.
Knowing Docker still matters. Portainer assumes you do. What it changes is the speed of the ordinary jobs: pulling a new image, restarting a service at 1 AM from your phone. Running it on a VPS gives it a public address and a certificate on port 9443, so that browser tab works from any network rather than only from your desk.